Apex Class & Business Logic Practice Problems

Problem Statement

Create a utility class TemperatureConverter with two static methods:

• celsiusToFahrenheit(Decimal c) → returns Decimal
• fahrenheitToCelsius(Decimal f) → returns Decimal

Formulas: F = C × 9/5 + 32  |  C = (F − 32) × 5/9

Constraints

• Handle null input — return null if input is null
• Round to 2 decimal places

Problem Statement

Create a class OpportunityHelper with a static method isWon(String stage) that returns true if the stage equals "Closed Won" (case-insensitive), otherwise false.

Also add isLost(String stage) that returns true for "Closed Lost".

Problem Statement

Create a class StringUtils with these static methods:

• isPalindrome(String s) — returns true if s reads the same forwards and backwards (ignore case)
• countWords(String s) — returns the number of words (split on whitespace)
• capitalizeFirst(String s) — capitalizes the first letter of every word

Problem Statement

Create a class MathHelper with these static methods:

• factorial(Integer n) — returns n! (use recursion or iteration)
• isPrime(Integer n) — returns true if n is prime
• fibonacci(Integer n) — returns the nth Fibonacci number (0-indexed)

Constraints

• Handle n ≤ 0 gracefully (return 0 for fibonacci, 1 for factorial, false for isPrime)

Problem Statement

Create a class AccountService with:

• getHotAccounts() — returns a List<Account> where Rating = 'Hot', ordered by Name
• deactivateSmallAccounts(Decimal maxRevenue) — sets Active__c = false on all Accounts with AnnualRevenue < maxRevenue, updates them, returns the count updated

Problem Statement

Create a class DiscountCalculator with a static method getDiscountedPrice(Decimal originalPrice, Integer quantity):

• Quantity 1–9 → 0% discount
• Quantity 10–49 → 10% discount
• Quantity 50–99 → 20% discount
• Quantity ≥ 100 → 30% discount

Returns the final price per unit after discount, rounded to 2 decimal places.

Problem Statement

Create a class RecordTypeHelper with a static method:

getId(String objectName, String developerName)

Returns the Id of the RecordType matching the given sObject name and developer name, or null if not found.

Must cache results in a static Map so subsequent calls for the same object don't trigger more SOQL.

Problem Statement

Create a class JsonParser with a static method parseContacts(String jsonStr) that parses a JSON array of objects like:

[{"name":"Alice","email":"alice@x.com"},{"name":"Bob","email":"bob@x.com"}]

Returns a List<Contact> with LastName set from name and Email set from email.

Problem Statement

Create a class HttpCalloutService with a method callWithRetry(String endpoint, Integer maxRetries).

It should make an HTTP GET request, and if the response status is not 200, retry up to maxRetries times with a 1-second delay between attempts.

Return the response body on success, or throw a CalloutException after all retries are exhausted.

Problem Statement

Create a Batch Apex class DeactivateOldContactsBatch that:

• Implements Database.Batchable<SObject>
• Queries all Contacts where LastActivityDate < 365 days ago
• Sets Active__c = false on each Contact in the execute method
• Has a finish method that sends an email summary

Problem Statement

Create a class AccountValidator with a custom exception InvalidAccountException (extends Exception).

Add a static method validate(Account acc) that throws InvalidAccountException if:

• Account Name is blank
• AnnualRevenue is negative

Returns true if valid.

Problem Statement

Create a Queueable Apex class WelcomeEmailQueueable that:

• Implements Queueable
• Accepts a List<Id> of Contact IDs in its constructor
• In execute(): queries the contacts, sends a welcome email to each
• Enqueued with System.enqueueJob()

Problem Statement

Implement a selector class ContactSelector following enterprise patterns:

• getByIds(Set<Id> ids) — returns Contacts by ID with standard fields
• getByAccountId(Id accountId) — returns Contacts for an Account
• getByEmail(String email) — returns a Contact matching the email

All queries must select: Id, FirstName, LastName, Email, Phone, AccountId

Problem Statement

Write an Apex class LeadScorer with a static method calculateScore that computes a numeric lead score based on attributes.

Scoring rules:

• Industry: Technology = +30, Finance = +25, Healthcare = +20, other = +10
• Annual Revenue: >= 10,000,000 = +40, >= 1,000,000 = +25, >= 100,000 = +10, else 0
• Employee Count: >= 1000 = +20, >= 100 = +10, else 0
• Has Phone: +5 if phone is not null/blank
• Has Email: +5 if email is not null/blank

Maximum possible score: 100

Method Signature

static Integer calculateScore(String industry, Decimal annualRevenue, Integer employees, String phone, String email)

Constraints

• All parameters may be null — treat null numeric fields as 0
• Return an Integer score (0–100)

Problem Statement

Write an Apex class StageValidator with a static method isValidTransition that enforces allowed stage progressions for Opportunities.

Allowed transitions:

• Prospecting → Qualification, Closed Lost
• Qualification → Needs Analysis, Closed Lost
• Needs Analysis → Value Proposition, Closed Lost
• Value Proposition → Id. Decision Makers, Closed Lost
• Id. Decision Makers → Perception Analysis, Closed Lost
• Perception Analysis → Proposal/Price Quote, Closed Lost
• Proposal/Price Quote → Negotiation/Review, Closed Lost
• Negotiation/Review → Closed Won, Closed Lost
• Closed Won → (no transitions allowed)
• Closed Lost → (no transitions allowed)

Method Signature

static Boolean isValidTransition(String fromStage, String toStage)

Constraints

• Return true only for explicitly listed transitions
• Staying in the same stage returns false
• Null inputs return false

Problem Statement

Write an Apex class TerritoryMapper with a static method getRegion that maps US state codes to sales regions.

Region mappings:

• Northeast: ME, NH, VT, MA, RI, CT, NY, NJ, PA
• Southeast: DE, MD, VA, WV, NC, SC, GA, FL, AL, MS, TN, KY, AR, LA
• Midwest: OH, IN, IL, MI, WI, MN, IA, MO, ND, SD, NE, KS
• Southwest: TX, OK, NM, AZ
• West: CO, WY, MT, ID, WA, OR, CA, NV, UT, AK, HI
• Unknown state codes return 'Unknown'

Method Signature

static String getRegion(String stateCode)

Constraints

• State codes are uppercase 2-letter abbreviations
• Null or blank input returns 'Unknown'
• Case-insensitive matching (normalize to uppercase)

Problem Statement

Create an Apex REST service that exposes Account data via HTTP endpoints.

Requirements:

• Annotate the class with @RestResource(urlMapping='/accounts/*')
• Implement a GET method annotated with @HttpGet that queries Accounts and returns them as a JSON-serializable list
• Implement a POST method annotated with @HttpPost that accepts an Account name in the request body and inserts a new Account
• Implement a DELETE method annotated with @HttpDelete that deletes an Account by ID from the URL parameter
• Use RestContext.request and RestContext.response where needed
• Return appropriate HTTP status codes (200, 201, 400, 404)

Constraints

• All methods must be global static
• Handle the case where the record is not found (404)
• Use try/catch for DML operations

Problem Statement

Build a robust HTTP callout handler class and its corresponding mock for testing.

Requirements for HttpCalloutHandler:

• A method fetchExternalData(String endpoint) that makes an HTTP GET callout
• Parse the JSON response into a wrapper class ApiResponse with fields: Integer statusCode, String body, Boolean success
• If status code is 200, set success = true; otherwise false
• Handle callout exceptions — set success=false, statusCode=500, body=exception message

Requirements for HttpCalloutHandlerMock:

• Implement the HttpCalloutMock interface
• Implement the respond method returning a mock 200 response

Constraints

• Use Http, HttpRequest, HttpResponse classes
• Set request timeout to 10000ms (10 seconds)

Problem Statement

Design a robust custom exception hierarchy for a payment processing service.

Requirements:

• Create a base exception PaymentException extending Exception
• Create subclasses:
  • InsufficientFundsException — includes Decimal balance and Decimal required fields
  • InvalidCardException — includes String cardType field
  • PaymentGatewayException — includes Integer errorCode and String gatewayMessage
• Write a PaymentProcessor class with method processPayment(Decimal amount, String cardType, Decimal accountBalance)
• Throw InvalidCardException if cardType is not in ('Visa','Mastercard','Amex')
• Throw InsufficientFundsException if accountBalance < amount
• Otherwise return true

Constraints

• Each custom exception must extend the appropriate parent
• Custom fields must be set via constructor or setter before throwing

Problem Statement

Write an Apex class StringUtils with a static method reverseWords(String sentence) that reverses the order of words in a sentence while preserving each word's characters.

Examples

• "Hello World Apex" → "Apex World Hello"
• "I love Salesforce" → "Salesforce love I"
• null or blank → ""

Method Signature

public static String reverseWords(String sentence)

Problem Statement

Write an Apex class WordCounter with a static method countWords(List<String> words) that returns a Map<String, Integer> counting the frequency of each word (case-insensitive).

Examples

• ['apex','java','apex','APEX'] → {apex:3, java:1}
• Empty list → empty map

Method Signature

public static Map<String, Integer> countWords(List<String> words)

Problem Statement

Write an Apex class MathUtils with a static method factorial(Integer n) that returns n!.

Rules

• 0! = 1 and 1! = 1
• 5! = 120
• Return -1 for negative inputs

Method Signature

public static Integer factorial(Integer n)

Problem Statement

Write an Apex class FizzBuzz with a static method generate(Integer n) that returns a List<String> of 1 through n with:

• Multiples of 3 → "Fizz"
• Multiples of 5 → "Buzz"
• Multiples of both → "FizzBuzz"
• Otherwise → the number as a String

Method Signature

public static List<String> generate(Integer n)

Problem Statement

Your sales operations team needs to automatically classify accounts into revenue tiers to determine service level agreements and pricing models.

Write an Apex class AccountTierService with a static method getRevenueTier(Decimal annualRevenue) that returns a tier label based on the account's annual revenue.

Tier Definitions

Method Signature

public static String getRevenueTier(Decimal annualRevenue)

Best Practices

• Always handle null input gracefully — null revenue maps to 'Bronze'.
• Use a single return per branch for clarity.

Problem Statement

Your finance team requires that discount approvals are routed to the correct authority level based on the percentage discount being offered on an opportunity.

Write an Apex class DiscountApprovalService with a static method getApprovalLevel(Decimal discountPercent) that returns the required approver.

Approval Matrix

Method Signature

public static String getApprovalLevel(Decimal discountPercent)

Problem Statement

Your account management team needs a single numeric health score (0–100) per account to prioritise outreach. The score is calculated from five weighted factors.

Write an Apex class AccountHealthService with a static method getHealthScore(String industry, Decimal annualRevenue, String rating, Integer contactCount, String billingState) that returns an Integer score.

Scoring Factors

• Annual Revenue (0–30 pts): ≥ $1M = 30 | ≥ $500K = 20 | ≥ $100K = 10 | else 0
• Rating (0–25 pts): 'Hot' = 25 | 'Warm' = 15 | 'Cold' = 5 | else 0
• Industry (10–20 pts): 'Technology' or 'Finance' = 20 | else 10
• Contact Count (0–15 pts): ≥ 10 = 15 | ≥ 5 = 10 | ≥ 1 = 5 | else 0
• Billing State (0–10 pts): non-null/non-blank = 10 | else 0

Method Signature

public static Integer getHealthScore(String industry, Decimal annualRevenue, String rating, Integer contactCount, String billingState)

Problem Statement

Write an Apex class LeadQualifier with a static method qualify(String source, Integer numEmployees, Decimal budget) that returns a letter grade based on company size and budget.

Grading Rules

• A — employees ≥ 1,000 OR budget ≥ 500,000
• B — employees ≥ 200 OR budget ≥ 100,000
• C — employees ≥ 50
• Unqualified — everything else

Requirements

• Null-safe: treat null employees or budget as 0
• Define thresholds as named constants (not magic numbers)
• Use with sharing on the class

Problem Statement

Write an Apex class InvoiceCalculator with a static method calculateTotal(List<Decimal> lineItems, Decimal taxRate, Decimal discountPct) that computes the final invoice total.

Formula

subtotal     = sum of all positive line items
afterDiscount = subtotal × (1 − discountPct ÷ 100)
total         = afterDiscount × (1 + taxRate ÷ 100)
Return total rounded to 2 decimal places.

Requirements

• Skip null or negative line items
• Treat null taxRate or discountPct as 0
• Return 0 for null or empty line-item list
• Round the result to 2 decimal places using .setScale(2)

Problem Statement

Write an Apex class PhoneFormatter with a static method formatPhone(String rawPhone) that formats any 10-digit US phone number into the standard (XXX) XXX-XXXX pattern.

Rules

• Strip all non-digit characters first (dashes, dots, spaces, parens)
• If the result is exactly 10 digits, format as (XXX) XXX-XXXX
• If not 10 digits, return the original input unchanged
• If blank or null, return ""

Examples

• "415-555-1234" → "(415) 555-1234"
• "4155551234" → "(415) 555-1234"
• "415.555.1234" → "(415) 555-1234"
• "12345" → "12345" (not 10 digits)

Problem Statement

Write an Apex class SLAChecker with a static method isBreached(String priority, Integer hoursOpen) that returns true when a case has exceeded its SLA time limit.

SLA Thresholds

Requirements

• Return false for null/blank priority or null hoursOpen
• Return false for unknown priority values
• Store thresholds in a Map constant — no if-else chains

Problem Statement

Write an Apex class NameFormatter with two static methods:

Method 1 — fullName

public static String fullName(String salutation, String firstName, String lastName)

Concatenates non-blank parts separated by a single space.
e.g. fullName("Mr.", "John", "Smith") → "Mr. John Smith"
e.g. fullName(null, "John", "Smith") → "John Smith"

Method 2 — lastFirst

public static String lastFirst(String firstName, String lastName)

Returns "Last, First" format.
e.g. lastFirst("John", "Smith") → "Smith, John"
e.g. lastFirst(null, "Smith") → "Smith"

Requirements

• Skip blank/null parts — do not produce leading/trailing spaces
• Use String.isBlank() for null-safe blank checks

Problem Statement

Write a service class ContactMergeService with a static method mergeContactsByAccount(Id accountId) that merges duplicate Contacts under the same Account.

Two Contacts are duplicates when they share the same full name (case-insensitive). The oldest Contact (earliest CreatedDate) is kept as the master record.

Requirements

• public with sharing class.
• Throw IllegalArgumentException when accountId is null.
• Query Contacts ordered by CreatedDate ASC; group by full name (case-insensitive).
• Call Database.merge(master, List<Id>) with up to 2 IDs per call.
• System.debug the merged count — visible in the Output tab.
• Return the total number of merged records.

Problem Statement

Write AccountHealthScoreService with two static methods:

• calculateHealthScore(Id accountId) — single-account wrapper that System.debugs the score.
• calculateHealthScores(Set<Id> accountIds) — bulk-safe: exactly 4 SOQL queries total.

Scoring Rules (0–100, clamped)

• +40 — open Opportunity
• +30 — Closed Won in last 12 months
• +20 — LastActivityDate within 90 days
• −30 — open Case

Business Scenario

Marketing wants every customer's Account to accumulate loyalty points whenever one of their Opportunities closes as Closed Won. Points are earned at a rate of 1 point per $100 of the won Amount, stored on a custom field Loyalty_Points__c (Number) on Account.

Requirements

• Build a reusable service method awardPoints(List<Opportunity> closedWonOpps) that a trigger can call with the Opportunities that just became Closed Won.
• Aggregate points per Account in memory first — one Opportunity may not be the only one closing for that Account in the same transaction.
• Query the affected Accounts in a single SOQL call and update all of them in a single DML call.

Best Practices

• No SOQL or DML inside a loop — collect Account Ids into a Set first, then query and update once outside any loop.
• WITH SECURITY_ENFORCED and a LIMIT on the query respect the running user's field/object-level security and cap the result size.
• Wrap the update in try/catch(DmlException) so a partial failure never throws an unhandled exception back to the caller.

Business Scenario

Sales wants a single, reusable place to compute the discount percentage a customer qualifies for, based on their Account.Type (standard picklist values such as Technology Partner and Reseller count as "partner" accounts) and AnnualRevenue.

Requirements

• Partner accounts (Technology Partner or Reseller) with revenue ≥ 1,000,000 get 20%; ≥ 250,000 get 15%; otherwise 10%.
• Non-partner accounts with revenue ≥ 1,000,000 get 10%; ≥ 250,000 get 5%; otherwise 0%.
• Null AnnualRevenue must be treated as 0, never throw an error.

Best Practices

• Use named constants for the revenue thresholds instead of bare numbers, so tuning the business rule later doesn't require hunting through comparison logic.
• Check the highest-value tiers first with early returns to keep the logic easy to read and avoid overlapping conditions.

Business Scenario

Operations wants Orders blocked before they're created if the requested quantity exceeds available inventory. Orders live on a custom object Order__c with a lookup Product__c to Product2 and a Quantity__c number field. Product2 has a custom Stock_Quantity__c field tracking units on hand.

Requirements

• Build validateStock(List<Order__c> ordersToInsert) that throws a custom exception when any product's total requested quantity across the batch exceeds its available stock.
• If the same product appears on multiple orders in the same batch, their quantities must be summed before comparing against stock.
• Look up current stock for every referenced product in a single query.

Best Practices

• No SOQL inside a loop — gather all Product Ids first, then query stock once.
• A custom Exception subclass communicates the specific failure reason clearly to the caller (e.g. a trigger) instead of a generic error.
• WITH SECURITY_ENFORCED and a LIMIT protect the query and respect field-level security on Stock_Quantity__c.

Business Scenario

Fulfillment needs a reusable utility to compute shipping charges consistently across the org. Orders live on the custom object Order__c, which carries Ship_Region__c (Text), Ship_Country__c (Text), and Weight_Kg__c (Number).

Requirements

• calculateShippingCharge(region, country, weightKg) returns a base rate (domestic USA vs. international) plus a per-kilogram charge, plus a surcharge for designated remote regions (Alaska, Hawaii, Remote Islands).
• Provide a bulk-friendly wrapper calculateShippingChargesForOrders(List<Order__c>) that returns a Map<Id, Decimal> of Order Id to computed charge.
• Treat missing weight or a null/blank country as safe defaults rather than throwing.

Best Practices

• All rates and the remote-region list are named constants, so Finance can adjust the pricing model in one place.
• The bulk method loops purely in memory (no SOQL/DML at all) — it is safe to call from inside a trigger for up to 200 records without any governor-limit risk.

Business Scenario

Management wants a dashboard-ready breakdown of Closed Won Opportunities by calendar month for a given date range — total count and total dollar amount per month, sorted chronologically.

Requirements

• Build getMonthlySummaries(Date startDate, Date endDate) returning a list of MonthSummary inner-class instances (month label, won count, total amount), sorted oldest month first.
• Only include Opportunities where StageName = 'Closed Won' and CloseDate falls within the given range (inclusive).
• Return an empty list for an invalid range (null dates or start after end) instead of throwing.

Best Practices

• A single SOQL query pulls all relevant Opportunities; monthly grouping is done in memory with a Map, avoiding any per-month query.
• WITH SECURITY_ENFORCED and a LIMIT keep the query safe and bounded for a reporting-style read.
• Sorting the month keys (formatted as YYYY-MM) guarantees a stable, chronological order regardless of the order records come back in.

Business Scenario

Support's SLA policy grants agents a number of business days (Monday through Friday) to resolve a Case, starting from when it was opened. Weekends must never count toward the SLA clock, or agents effectively lose time they were promised.

Requirements

• Build calculateDueDate(Datetime startDateTime, Integer businessDays) that advances one calendar day at a time, only counting weekdays, until businessDays weekdays have been added.
• Saturday and Sunday must be skipped entirely — they never count and the due date itself should never land on one (advancing day-by-day naturally guarantees this).
• Invalid input (null start, null/zero/negative businessDays) should return the original startDateTime unchanged rather than throwing.

Best Practices

• Datetime.format('u') returns the ISO day-of-week ('1' Monday through '7' Sunday) without any manual modulo-arithmetic date math, which is easy to get off-by-one.
• Isolating the weekend check into its own isWeekend helper keeps the day-counting loop readable and makes the rule easy to unit test in isolation.

Business Scenario

Finance needs a single Apex service that computes tax for an order's taxable amount, but the calculation rules differ per country: some use a flat percentage, others use progressive tiers based on the amount. New countries are added periodically, and the rules should not require rewriting a giant if/else chain each time.

Requirements

• Define a TaxStrategy interface with one method, calculateTax(Decimal taxableAmount).
• Implement at least FlatRateTaxStrategy (a single percentage) and TieredTaxStrategy (rate depends on which threshold the amount clears).
• Expose a single entry point calculateTax(String countryCode, Decimal taxableAmount) that looks up the right strategy for the country and delegates to it, falling back to a default strategy for unrecognized countries.

Best Practices

• The Strategy pattern (an interface + a Map of country to implementation) lets new tax rules be added by registering a new strategy instance, without touching existing logic — this is the reusability the scenario calls for.
• Every strategy is null-safe on its input and rounds the result with setScale(2) for currency-correct output.

Business Scenario

Revenue operations wants product pricing to automatically flex based on the purchasing Account's customer segment (Enterprise, Mid-Market, or SMB, tracked on a custom Account field Customer_Segment__c) and a seasonal peak surcharge that applies during November and December.

Requirements

• Build calculatePrice(Decimal listPrice, String customerSegment, Date effectiveDate).
• Apply a segment discount first (Enterprise 20%, Mid-Market 10%, SMB 5%, unrecognized segments get no discount), then apply an 8% peak-season surcharge if effectiveDate falls in November or December.
• Null listPrice must be treated as 0 rather than throwing a null pointer exception.

Best Practices

• Segment discount lookup is isolated into its own private helper method, keeping calculatePrice focused on the overall pricing sequence (discount, then surcharge) rather than a long nested conditional.
• All percentages are named constants so Finance-driven rate changes are a one-line edit, not a hunt through arithmetic expressions.

Business Scenario

HR wants a configurable bonus calculation for the custom object Employee__c (fields Salary__c, Performance_Rating__c 1-5, and Years_Of_Service__c). Bonuses combine a performance component and a capped loyalty component, but only employees who meet a minimum performance bar qualify at all.

Requirements

• Employees rated below 3 receive no bonus at all.
• Performance bonus: 2% of salary per rating point (e.g. rating 4 → 8%).
• Loyalty bonus: 0.5% of salary per year of service, capped at 5% regardless of tenure.
• Total bonus = (performance % + loyalty %) × salary, and provide a bulk wrapper returning a Map<Id, Decimal> for a list of employees.

Best Practices

• Every rate and threshold (rating cutoff, per-point/per-year percentages, loyalty cap) is a named constant, since HR routinely renegotiates these business rules.
• The single-employee method is pure and side-effect free, so it can be reused directly by both a bulk wrapper and, e.g., a preview UI — no SOQL or DML lives inside it.

Business Scenario

Multiple objects (Account billing address, Contact mailing address, a future Order shipping address) all need the same address-quality checks before being saved. Build one reusable service so the validation rules live in exactly one place.

Requirements

• validateAddress(street, city, state, postalCode, country) returns a ValidationResult inner class holding isValid and a list of human-readable errors.
• Street and city are always required. For US addresses (country is USA/US/blank), the state must be a valid 2-letter code and the postal code must match US ZIP format (12345 or 12345-6789).
• Non-US addresses only require a non-blank postal code.
• Provide a bulk wrapper validateAccounts(List<Account>) returning a Map<Id, ValidationResult> for the standard Account billing address fields.

Best Practices

• Accepting individual field values (rather than a specific SObject type) is what makes validateAddress reusable across Account, Contact, and any future object — the bulk wrapper adapts a specific SObject's fields to that generic signature.
• Collecting every failure into a list (instead of stopping at the first error) gives the caller the full picture in one pass, which is friendlier for a UI or bulk import.

Business Scenario

Customer Success wants renewal quotes computed automatically for the custom object Subscription__c (Base_Amount__c, Consecutive_Renewals__c, Auto_Renew__c checkbox, Contract_Term_Months__c). Multiple discounts can stack: loyalty (more consecutive renewals = bigger discount, capped), auto-renew enrollment, and committing to an annual-or-longer term.

Requirements

• Loyalty discount: 2% per consecutive renewal, capped at 10% total.
• Auto-renew discount: flat additional 5% if Auto_Renew__c is true.
• Annual term discount: flat additional 8% if Contract_Term_Months__c >= 12.
• All applicable discounts stack additively against the base amount, then apply once. Provide both a single-subscription method and a bulk Map<Id, Decimal> wrapper.

Best Practices

• Math.min() enforces the loyalty discount cap cleanly instead of a manual if-check, and keeps the cap logic in one expression.
• Discounts are summed into a single totalDiscountPct and applied once at the end — avoids compounding rounding errors from applying each discount sequentially to an already-discounted amount.
• All rates and caps are named constants for easy business-rule tuning.

Business Scenario

Sales wants a "customers who bought this also bought that" recommendation feature for an Account's product page: given an Account, suggest up to 5 Products that similar customers purchased but this Account has not, ranked by how often those similar customers bought each candidate product.

Requirements

• Build getRecommendations(Id accountId) returning up to 5 Product2 records.
• Step 1: find products this Account has already purchased (Closed Won OpportunityLineItems).
• Step 2: find other Accounts ("similar accounts") that purchased at least one of the same products.
• Step 3: among those similar accounts' other purchases (excluding products this Account already owns), rank candidate products by purchase frequency and return the top 5.

Best Practices

• Each stage of the algorithm is a single aggregate SOQL query — no per-record queries inside a loop, even though the logic spans three distinct steps.
• WITH SECURITY_ENFORCED and a LIMIT on every query keeps each stage safe and bounded regardless of how large the customer base grows.
• Early-return guard clauses after each stage (no purchases, no similar accounts, no co-occurring products) avoid unnecessary downstream queries when there is nothing left to compute.

Business Scenario

Finance wants a Closed Won revenue report broken down by fiscal quarter, where the fiscal year does not necessarily start in January — the org's fiscal year start month is a configurable input (e.g. 2 means the fiscal year runs February through January).

Requirements

• Build getQuarterlyReport(Integer year, Integer fiscalYearStartMonth) returning exactly four QuarterSummary entries (Q1-Q4) — total revenue and deal count of Closed Won Opportunities closing in that fiscal quarter.
• Compute the fiscal year's date boundaries from fiscalYearStartMonth, then bucket each Opportunity's CloseDate into one of the four 3-month quarters relative to that start.
• Default fiscalYearStartMonth to January (1) when not supplied.

Best Practices

• A single SOQL query pulls every Closed Won Opportunity in the fiscal year; quarter bucketing is pure in-memory arithmetic, avoiding four separate per-quarter queries.
• WITH SECURITY_ENFORCED and a LIMIT keep this reporting-style query safe and bounded.
• Pre-seeding summaryByQuarter with all four quarters before the loop guarantees the report always returns Q1-Q4 even for quarters with zero deals.

Business Scenario

Multiple triggers across the org (Case escalations, Opportunity stage changes, Contract renewals) all need to notify a user, but some notifications should be emails and others should be follow-up Tasks. Build one generic notification service so trigger code never has to know the delivery mechanism.

Requirements

• Define a NotificationChannel interface with send(String recipientId, String subject, String body).
• Implement EmailChannel (using Messaging.SingleEmailMessage targeted at a User/Contact Id) and TaskChannel (creating a Task owned by the recipient).
• Expose notify(NotificationChannel channel, String recipientId, String subject, String body) as the generic entry point, plus a bulk notifyMultiple(..., List<String> recipientIds, ...) for sending the same message to many recipients.

Best Practices

• The NotificationChannel interface decouples "who is calling" from "how the message is delivered" — a new channel (e.g. Chatter post, SMS) can be added without touching any existing trigger.
• Each channel implementation wraps its own DML/callout in try/catch (EmailException for email, DmlException for the Task insert) so a delivery failure never bubbles up as an unhandled exception to the caller.

Problem Statement

Write an Apex class WorkingDaysCalculator with a static method countWorkingDays(Date startDate, Date endDate) that returns the number of weekdays (Monday through Friday) in the range from startDate to endDate, inclusive of both ends.

Rules

• Weekends (Saturday, Sunday) are never counted.
• If startDate or endDate is null, or startDate is after endDate, return 0.

Hint on Day-of-Week

Apex's Date class has no built-in "day of week" method. The standard technique: pick any date whose weekday you know for certain, then use Date.daysBetween() together with Math.mod() to find the offset from that reference day.

Method Signature

public static Integer countWorkingDays(Date startDate, Date endDate)

Problem Statement

Write an Apex class DurationFormatter with a static method formatDuration(Integer totalSeconds) that converts a duration in seconds into a human-readable string.

Format Rules

• Always show seconds, e.g. "45s".
• Show minutes if there is at least 1 full minute (or at least 1 hour), e.g. "2m 5s".
• Show hours only if there is at least 1 full hour, e.g. "1h 1m 1s".
• null or a negative number returns "0s".

Examples

• 3661 → "1h 1m 1s"
• 125 → "2m 5s"
• 45 → "45s"
• 0 → "0s"

Method Signature

public static String formatDuration(Integer totalSeconds)

Problem Statement

Write an Apex class FrequencyAnalyzer with a static method mostFrequent(List<Integer> nums) that returns the value that appears most often in the list.

Rules

• If there is a tie for the highest frequency, return whichever tied value appears first in the input list.
• null or an empty list returns null.

Examples

• [1, 2, 2, 3, 3, 2] → 2 (three occurrences)
• [5, 5, 7, 7] → 5 (tied at 2 each, 5 appears first)

Method Signature

public static Integer mostFrequent(List<Integer> nums)

Problem Statement

Write an Apex class DedupUtil with a static method removeConsecutiveDuplicates(List<String> items) that collapses runs of consecutive equal values down to a single occurrence (similar to the Unix uniq command). Non-consecutive repeats are left alone.

Examples

• ['a','a','b','b','b','a'] → ['a','b','a']
• ['x','y','x'] → ['x','y','x'] (no consecutive repeats)

null returns an empty list.

Method Signature

public static List<String> removeConsecutiveDuplicates(List<String> items)

Problem Statement

Write an Apex class SetUtil with a static method findCommon(Set<String> setA, Set<String> setB) that returns a new Set<String> containing only the values present in both sets (their intersection).

A null set is treated as empty.

Method Signature

public static Set<String> findCommon(Set<String> setA, Set<String> setB)

Problem Statement

Write an Apex class SequenceGenerator with a static method generateSequence(Integer start, Integer end, Integer step) that returns a List<Integer> starting at start, increasing by step each time, up to and including end.

Rules

• If step is null or not positive, return an empty list.
• If start is after end, return an empty list.

Examples

• (1, 10, 2) → [1, 3, 5, 7, 9]
• (5, 5, 1) → [5]

Method Signature

public static List<Integer> generateSequence(Integer start, Integer end, Integer step)

Problem Statement

Write an Apex class StringValidator with a static method isAlphanumeric(String input) that returns true only if every character in input is a letter (A-Z, a-z) or a digit (0-9), and the string is non-empty.

null or an empty string returns false.

Method Signature

public static Boolean isAlphanumeric(String input)

Problem Statement

Write an Apex class DelimitedStringParser with a static method toValueSet(String csv, String delimiter) that splits csv on delimiter, trims whitespace from each piece, discards any blank pieces, and returns the unique remaining values as a Set<String>.

null or blank csv returns an empty set.

Example

toValueSet(" a, b ,c,, a", ",") → {'a', 'b', 'c'}

Method Signature

public static Set<String> toValueSet(String csv, String delimiter)

Problem Statement

Write an Apex class InvestmentCalculator with a static method calculateCompoundInterest(Decimal principal, Decimal annualRatePercent, Integer years) that returns the final investment value after compounding annually for the given number of years, rounded to 2 decimal places.

Formula: finalAmount = principal * (1 + rate/100)^years

Invalid input (any null argument, or negative years) returns 0.

Method Signature

public static Decimal calculateCompoundInterest(Decimal principal, Decimal annualRatePercent, Integer years)

Problem Statement

Write an Apex class ShippingEstimator with two static methods:

• getZoneDays(String zone) — returns the number of delivery days for a zone: 'LOCAL' → 2, 'REGIONAL' → 5, 'INTERNATIONAL' → 10. Any other value (including null) returns null.
• calculateETA(Date orderDate, String zone) — returns orderDate plus the zone's delivery days. If the zone is unrecognized or either argument is null, returns null.

Method Signatures

public static Integer getZoneDays(String zone)
public static Date calculateETA(Date orderDate, String zone)

Problem Statement

Write a REST resource CustomerPreferenceResource exposed at /CustomerPreferences/* that accepts a GET request with the Account Id as the URL suffix, and returns that account's Communication_Preference__c and Marketing_Opt_In__c as JSON. A missing or unknown Id returns a 404.

Problem Statement

Write a REST resource ProductAvailabilityResource at /ProductAvailability accepting a POST with a JSON body {"productIds": [...]}, and responding with each product's Id and QuantityOnHand__c as a JSON array — bulk-safe for any number of Ids in one request.

Problem Statement

Write a REST resource PagedAccountResource at /Accounts supporting GET with page and pageSize query parameters, returning that page of Accounts along with totalRecords and totalPages in the response JSON.

Problem Statement

Write a REST resource LeadIntakeResource at /LeadIntake accepting a POST with {"email": "...", "company": "..."}. If either field is missing or blank, respond with status 400 and a standardized body {"error": "...", "field": "..."} naming the first missing field — never let an unhandled exception escape.

Problem Statement

Write a REST resource OrderSubmissionResource at /OrderSubmission accepting a POST with {"idempotencyKey": "...", "accountId": "...", "totalAmount": ...}. If an Order already exists with that Idempotency_Key__c, return the existing order's Id with status 200 instead of creating a duplicate; otherwise insert a new one and return 201. A failed insert (e.g. a validation rule rejecting the order) must return status 500 with an error body, never an unhandled exception.

Problem Statement

Write an Apex class ProductCatalogParser with a static method parseCatalog(String jsonString) that parses a nested JSON product catalog (shape: {"products": [{"name":..., "sku":..., "pricing": {"listPrice":...}}]}) into a flat List<Map<String, Object>>, each entry holding name, sku, and listPrice pulled up from the nested pricing object.

A product missing the pricing object entirely gets a null listPrice, not an error.

Method Signature

public static List<Map<String, Object>> parseCatalog(String jsonString)