/** * File: two_sum.js * Created Time: 2022-12-15 * Author: gyt95 (gytkwan@gmail.com) */ /* Method one: Brute force enumeration */ function twoSumBruteForce(nums, target) { const n = nums.length; // Two-layer loop, time complexity is O(n^2) for (let i = 0; i < n; i++) { for (let j = i + 1; j < n; j++) { if (nums[i] + nums[j] === target) { return [i, j]; } } } return []; } /* Method two: Auxiliary hash table */ function twoSumHashTable(nums, target) { // Auxiliary hash table, space complexity is O(n) let m = {}; // Single-layer loop, time complexity is O(n) for (let i = 0; i < nums.length; i++) { if (m[target - nums[i]] !== undefined) { return [m[target - nums[i]], i]; } else { m[nums[i]] = i; } } return []; } /* Driver Code */ // Method one const nums = [2, 7, 11, 15], target = 13; let res = twoSumBruteForce(nums, target); console.log('Method one res =', res); // Method two res = twoSumHashTable(nums, target); console.log('Method two res =', res);