leetcode：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].

用hash表，O(N)的解法

/**
* @param {number[]} nums
* @param {number} target
* @return {number[]}
*/
var twoSum = function(nums, target) {
var map = {};
for(var i = 0; i < nums.length; i++) {
var need = target - nums[i];
if(typeof map[need] === 'number') {
return [map[need], i];
} else {
map[nums[i]] = i;
}
}
};