1.Two Sum Leet Code Problems Solutions using JavaScript, Typescript, Python

QUESTION; -

Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

You can return the answer in any order.

Example 1:

Input: nums = [2,7,11,15], target = 9
Output: [0,1]
Explanation: Because nums[0] + nums[1] == 9, we return [0, 1].

Example 2:

Input: nums = [3,2,4], target = 6
Output: [1,2]

Example 3:

Input: nums = [3,3], target = 6
Output: [0,1]
 

Constraints:

2 <= nums.length <= 104
-109 <= nums[i] <= 109
-109 <= target <= 109
Only one valid answer exists.
 

Follow-up: Can you come up with an algorithm that is less than O(n2) time complexity?

Answer

Using Typescript

function twoSum(nums: number[], target: number): number[] {
     const numIndexMap: { [key: number]: number } = {}; // Maps numbers to their indices

    // Traverse the array
    for (let i = 0; i < nums.length; i++) {
        const num = nums[i];
        const complement = target - num;

        // Check if the complement exists in the hashmap
        if (complement in numIndexMap) {
            // Return the indices of the current number and its complement
            return [numIndexMap[complement], i];
        }

        // Otherwise, add the current number and its index to the hashmap
        numIndexMap[num] = i;
    }

    // If no solution is found
    return [];
};

// Test cases
const nums1: number[] = [2, 7, 11, 15];
const target1: number = 9;
console.log(twoSum(nums1, target1)); // Output: [0, 1]

const nums2: number[] = [3, 2, 4];
const target2: number = 6;
console.log(twoSum(nums2, target2)); // Output: [1, 2]

const nums3: number[] = [3, 3];
const target3: number = 6;
console.log(twoSum(nums3, target3)); // Output: [0, 1]

Using JavaScript.

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[]}
 */
var twoSum = function(nums, target) {
      const numIndexMap = {}; // Maps numbers to their indices
   
    // Traverse the array
    for (let i = 0; i < nums.length; i++) {
        const num = nums[i];
        const complement = target - num;

        // Check if the complement exists in the hashmap
        if (numIndexMap[complement] !== undefined) {
            // Return the indices of the current number and its complement
            return [numIndexMap[complement], i];
        }

        // Otherwise, add the current number and its index to the hashmap
        numIndexMap[num] = i;
    }

    // If no solution is found
    return [];
};

// Test cases
const nums1 = [2, 7, 11, 15];
const target1 = 9;
console.log(twoSum(nums1, target1)); // Output: [0, 1]

const nums2 = [3, 2, 4];
const target2 = 6;
console.log(twoSum(nums2, target2)); // Output: [1, 2]

const nums3 = [3, 3];
const target3 = 6;
console.log(twoSum(nums3, target3)); // Output: [0, 1]