C++ Coding Test Course, Why is Debugging Important?

The coding test is an important process that evaluates not only understanding of programming languages but also problem-solving abilities. C++ is an efficient and powerful language, and many companies use C++-based coding tests to assess candidates. In this article, I will introduce an algorithm problem from a C++ coding test and explain the process of solving it in detail. I will also provide an in-depth discussion on the importance of debugging.

Problem: Sum of Two Numbers in an Array

Problem Description: Given an integer array nums and an integer target, write a function that returns the indices of the two numbers in the nums array that add up to target. It is assumed that each input has exactly one solution and you may not use the same element twice.

Input

  • nums: integer array
  • target: integer

Output

Returns an array of corresponding indices. For example, given nums = [2, 7, 11, 15] and target = 9, it should return [0, 1].

Problem-Solving Process

1. Problem Analysis

Before solving the problem, it is important to thoroughly understand it. The key is to find the indices of the specific numbers. While scanning the given array, you need to check if using each number can lead to the target number. For example, if the sum of two numbers equals the target, you need to find the indices of those two numbers.

2. Approach

This problem can be approached in several ways. The most basic method is to use two nested loops. However, this increases the time complexity to O(n^2), making it inefficient. Therefore, a HashMap can be used to improve the access speed. By using a HashMap, you can store previously checked numbers and find the number needed to reach the target with the current number in one go.

3. Code Implementation

#include <iostream>
#include <vector>
#include <unordered_map>

std::vector<int> twoSum(std::vector<int> &nums, int target) {
    std::unordered_map<int, int> map; // HashMap to store numbers and indices
    for (int i = 0; i < nums.size(); ++i) {
        int complement = target - nums[i]; // Number needed when using the current number
        if (map.find(complement) != map.end()) { // Check if the number exists in the HashMap
            return {map[complement], i}; // Return indices
        }
        map[nums[i]] = i; // Store the current number in the HashMap
    }
    return {}; // Return if no result
}

int main() {
    std::vector<int> nums = {2, 7, 11, 15};
    int target = 9;
    std::vector<int> result = twoSum(nums, target);
    std::cout << "Result: " << result[0] << ", " << result[1] << std::endl;
    return 0;
}

4. Code Explanation

The code has the following structure:

  • Uses unordered_map to store each number and its index.
  • Iterates through the array with a for loop. In each iteration, it compares the current number with complement.
  • If map contains complement, the result is returned immediately.
  • If not, the current number and index are stored in the map.

5. Debugging Process

After writing the code, it is essential to find errors through the debugging process. The reasons why debugging is important are:

  • Finding Errors: Debugging can help easily identify logical and syntax errors.
  • Code Improvement: By fixing identified errors, you can improve the quality and performance of the code.
  • Self-Check: In the review process, you can discover other enhancements or optimization opportunities.

Techniques for debugging include:

  • Using Print Statements: Adding print statements to specific parts of the code to check how values change.
  • Using Debugging Tools: Utilizing IDE debugging tools to run the program step by step.
  • Unit Testing: Testing functions against multiple input cases to verify all possibilities.

6. Conclusion

In this blog, we examined the problem-solving process in detail through an example of a C++ coding test. Along with the problem-solving process, we discussed the significance of debugging, providing direction in the coding and modification process. Coding tests go beyond merely writing code; they involve understanding the problem and finding solutions, requiring such approaches. Remember not to forget the process of finding errors and improving performance through debugging.

In the future, I will cover additional concepts and algorithm problems related to C++ to help enhance your coding skills. Thank you!