0001. Two Sum.md

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.

Array

1. Very straightforward O(n^2) solution

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[]}
 */
var twoSum = function(nums, target) {
    for(let i = 0; i < nums.length; i++) {
        for(let j = i + 1; j < nums.length; j++) {
            if(nums[i] + nums[j] === target) {
                return [i, j];
            }
        }
    }
};

2. Hashmap O(n) solution

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[]}
 */

// O(n) hashmap solution
var twoSum = function(nums, target) {
    let map = new Map();
    for(let i = 0; i < nums.length; i++) {
        if(map.has(target - nums[i])) {
            // map.get will get the 1st number index and current number index
            return [map.get(target - nums[i]), i];
        }
        // set the number and its index
        map.set(nums[i], i)
    }
    return [];
}