JavaScript Coding Test Course, Hacking Effectively

JavaScript is one of the most important languages in web development, and its significance is further highlighted in algorithm problem solving. Many companies evaluate applicants’ problem-solving skills and coding abilities through coding tests. This article will detail the overall approach to coding tests and the problem-solving process through algorithm problems that can be solved with JavaScript.

Problem Description

Problem 1: Sum of Two Numbers

Given an integer array nums and an integer target, write a function that returns the indices of the two numbers in the array that add up to target.

For example:

  • If nums = [2, 7, 11, 15] and target = 9, it should return [0, 1]. (2 + 7 = 9)

Approach to the Problem

To solve this problem, you can take the following approach.

  1. Using a nested loop: This method involves iterating through the two elements of the array to calculate the sum. However, the time complexity is O(n2), making it inefficient.
  2. Using a hashmap: This allows solving the problem in one pass. You store the required numbers in a hashmap and check if the difference between the current number and the target exists in the hashmap. The time complexity of this method is O(n).

Solution: Code using Hashmap

function twoSum(nums, target) {
    const map = new Map(); // Initialize the hashmap

    for (let i = 0; i < nums.length; i++) {
        const complement = target - nums[i]; // Calculate the required value

        if (map.has(complement)) {
            return [map.get(complement), i]; // Return the indices
        }
        
        map.set(nums[i], i); // Add the current number to the hashmap
    }
    
    return []; // Return an empty array if no result is found
}

Code Explanation

The code above defines the twoSum function. The function takes two parameters: an integer array nums and an integer target.

  1. Initialize the hashmap (map).
  2. Iterate through the given array nums.
  3. Calculate the complement for each number. (The result of subtracting the current value from the target value)
  4. Check if the hashmap contains the complement. If it does, return the current index and the stored index.
  5. Add the current number to the hashmap.

Review

Using a hashmap to solve the problem was efficient. The reason is that the code operates with a complexity of O(n), allowing it to respond quickly to all input cases. By solving various problems and understanding the solutions while preparing for coding tests, you can gain a deep understanding of algorithms and data structures.

Conclusion

Success in JavaScript coding tests relies on the ability to read and understand problems, as well as the ability to select appropriate algorithms. The sum of two numbers problem discussed today is not particularly complex, but it serves as good practice for developing algorithmic thinking. Keep solving more problems to improve your skills!