Capital One Coding Questions - DSA Problems & Solutions

Company Overview

This page contains Capital One coding questions from Capital One OA placement papers with detailed solutions.

Coding Focus

Capital One OA coding section includes 2-3 problems focusing on DSA and financial technology concepts. Master arrays, trees, graphs, and system design to succeed.

Capital One Coding Questions Overview

Capital One OA Coding Section:

• Problems: 2-3 coding problems
• Time: 90 minutes
• Languages: Java, Python

Coding Problems

Question 1: Credit Card Fraud Detection

Q1: Detect fraudulent credit card transactions using pattern matching.

Solution (Java):

public List<String> detectFraud(List<Transaction> transactions) {
    List<String> frauds = new ArrayList<>();
    Map<String, List<Transaction>> userTransactions = new HashMap<>();

    for (Transaction txn : transactions) {
        userTransactions.putIfAbsent(txn.userId, new ArrayList<>());
        userTransactions.get(txn.userId).add(txn);
    }

    for (String userId : userTransactions.keySet()) {
        List<Transaction> txns = userTransactions.get(userId);
        if (txns.size() > 10) {
            // Check for unusual patterns
            double avgAmount = txns.stream()
                .mapToDouble(t -> t.amount).average().orElse(0);
            for (Transaction txn : txns) {
                if (txn.amount > avgAmount * 3) {
                    frauds.add(txn.transactionId);
                }
            }
        }
    }

    return frauds;
}

Time Complexity: O(n)

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