1. Two Sum

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.

Solution

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[]}
 */
var twoSum = function(nums, target) {
    var len = nums.length;
    var result = [];
    var hash = [];
    for (var i = 0; i< len; i++) {
        if (hash[target - nums[i]] !== undefined) {
            result[0] = hash[target - nums[i]];
            result[1] = i;
            return result;
        } else {
            hash[nums[i]] = i;
        }
    }
};