LeetCode 1. Two Sum

Problem:

Given an array of integers, return indices of the two numbers such that they add up to a specific target.

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

Example:

Input: nums = [2,7,11,15], target = 9

Output: [0,1]

Output: Because nums[0] + nums[1] == 9, we return [0, 1].

Idea:

Hashtable

Solution:

Hashtable / Javascript

Time complexity: O(n)

Space complexity: O(n)

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[]}
 */
var twoSum = function(nums, target) {
    let map = new Map();
    
    for (let i = 0; i < nums.length; i++) {
        let diff = target - nums[i];
        if (map.has(diff)) {
            return [i, map.get(diff)];
        } else {
            map.set(nums[i],i);
        }
    }
};