Technical Interview Strategy & Mock Questions

1// Interview Coding Exercises
2
3// 1. CLASSIC: Write a bulkified trigger
4// Prompt: "Write a trigger that updates the Account's total revenue 
5//          when Opportunities are inserted or updated."
6
7trigger OpportunityTrigger on Opportunity (after insert, after update) {
8    // Collect affected Account IDs
9    Set<Id> accountIds = new Set<Id>();
10    for (Opportunity opp : Trigger.new) {
11        if (opp.AccountId != null) {
12            accountIds.add(opp.AccountId);
13        }
14    }
15    // Also check old values for reparented opps
16    if (Trigger.isUpdate) {
17        for (Opportunity opp : Trigger.old) {
18            if (opp.AccountId != null) {
19                accountIds.add(opp.AccountId);
20            }
21        }
22    }
23    
24    if (accountIds.isEmpty()) return;
25    
26    // Aggregate opportunity amounts per account
27    Map<Id, Decimal> revenueByAccount = new Map<Id, Decimal>();
28    for (AggregateResult ar : [
29        SELECT AccountId, SUM(Amount) totalAmount
30        FROM Opportunity
31        WHERE AccountId IN :accountIds
32        AND StageName = 'Closed Won'
33        GROUP BY AccountId
34    ]) {
35        revenueByAccount.put(
36            (Id) ar.get('AccountId'), 
37            (Decimal) ar.get('totalAmount')
38        );
39    }
40    
41    // Update accounts
42    List<Account> accountsToUpdate = new List<Account>();
43    for (Id accId : accountIds) {
44        accountsToUpdate.add(new Account(
45            Id = accId,
46            Total_Revenue__c = revenueByAccount.containsKey(accId) 
47                ? revenueByAccount.get(accId) : 0
48        ));
49    }
50    update accountsToUpdate;
51}
52
53// 2. CODE REVIEW: Find and fix all issues in this code
54// Prompt: "Review this code and identify all problems"
55
56/*
57 BUGGY CODE (find the issues):
58
59 trigger CaseTrigger on Case (after insert) {
60     for (Case c : Trigger.new) {
61         Account acc = [SELECT Id, Name FROM Account WHERE Id = :c.AccountId];
62         c.Description = 'Account: ' + acc.Name;
63         update c;
64         
65         EmailService.sendEmail(c.ContactEmail, 'Case Created', c.Subject);
66         
67         Task t = new Task();
68         t.WhatId = c.Id;
69         t.Subject = 'Follow up';
70         insert t;
71     }
72 }
73
74 ISSUES:
75 1. SOQL inside loop — will fail at 101 records
76 2. DML inside loop (update c) — will fail at 151 records
77 3. Cannot modify Trigger.new in after trigger (read-only)
78 4. DML inside loop (insert t) — another DML per iteration
79 5. Email in loop — will hit email invocation limit
80 6. No null check on AccountId
81 7. No error handling
82 8. Single trigger, should use handler pattern
83*/
84
85// FIXED VERSION:
86public class CaseTriggerHandler {
87    
88    public static void handleAfterInsert(List<Case> cases) {
89        // Collect data
90        Set<Id> accountIds = new Set<Id>();
91        for (Case c : cases) {
92            if (c.AccountId != null) accountIds.add(c.AccountId);
93        }
94        
95        // Query once
96        Map<Id, Account> accounts = new Map<Id, Account>(
97            [SELECT Id, Name FROM Account WHERE Id IN :accountIds]
98        );
99        
100        // Process
101        List<Case> casesToUpdate = new List<Case>();
102        List<Task> tasksToCreate = new List<Task>();
103        List<Messaging.SingleEmailMessage> emails = new List<Messaging.SingleEmailMessage>();
104        
105        for (Case c : cases) {
106            // Update case description
107            Account acc = accounts.get(c.AccountId);
108            if (acc != null) {
109                casesToUpdate.add(new Case(
110                    Id = c.Id,
111                    Description = 'Account: ' + acc.Name
112                ));
113            }
114            
115            // Create follow-up task
116            tasksToCreate.add(new Task(
117                WhatId = c.Id,
118                Subject = 'Follow up on case: ' + c.CaseNumber,
119                ActivityDate = Date.today().addDays(1)
120            ));
121        }
122        
123        // DML once each
124        if (!casesToUpdate.isEmpty()) update casesToUpdate;
125        if (!tasksToCreate.isEmpty()) insert tasksToCreate;
126    }
127}
128
129// 3. SYSTEM DESIGN: Design a Lead scoring system
130// Prompt: "Design a system that scores Leads based on behavior and demographics"
131
132public class LeadScoringEngine {
133    
134    // Configuration-driven scoring via Custom Metadata
135    public static void scoreLeads(List<Lead> leads) {
136        // Load scoring rules from Custom Metadata
137        List<Lead_Score_Rule__mdt> rules = [
138            SELECT Category__c, Field_Name__c, Operator__c, 
139                   Value__c, Points__c
140            FROM Lead_Score_Rule__mdt
141            WHERE Is_Active__c = true
142        ];
143        
144        for (Lead lead : leads) {
145            Integer score = 0;
146            
147            for (Lead_Score_Rule__mdt rule : rules) {
148                if (evaluateRule(lead, rule)) {
149                    score += (Integer) rule.Points__c;
150                }
151            }
152            
153            lead.Lead_Score__c = score;
154            lead.Score_Grade__c = getGrade(score);
155        }
156    }
157    
158    private static Boolean evaluateRule(Lead lead, Lead_Score_Rule__mdt rule) {
159        Object fieldValue = lead.get(rule.Field_Name__c);
160        if (fieldValue == null) return false;
161        
162        String valueStr = String.valueOf(fieldValue);
163        
164        switch on rule.Operator__c {
165            when 'equals' { return valueStr == rule.Value__c; }
166            when 'contains' { return valueStr.contains(rule.Value__c); }
167            when 'not_empty' { return String.isNotBlank(valueStr); }
168            when else { return false; }
169        }
170    }
171    
172    private static String getGrade(Integer score) {
173        if (score >= 80) return 'A';
174        if (score >= 60) return 'B';
175        if (score >= 40) return 'C';
176        if (score >= 20) return 'D';
177        return 'F';
178    }
179}