1 Two Sum.js

// 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.

// Example:
// Given nums = [2, 7, 11, 15], target = 9,

// Because nums[0] + nums[1] = 2 + 7 = 9,
// return [0, 1].
// UPDATE (2016/2/13):
// The return format had been changed to zero-based indices. Please read the above updated description carefully.

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/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[]}
 */
var twoSum = function(nums, target) {
    var hash = {};
    
    for(var i = 0; i < nums.length; i++) {
        var num = nums[i];
        if(hash[num] !== undefined) {
            return [hash[num], i]
        } else {
            hash[target - num] = i;
        }
    }
    
    return [];
};