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:

Given nums = [2, 7, 11, 15], target = 9,Because nums[0] + nums[1] = 2 + 7 = 9,return [0, 1].

solution1:

时间复杂度O(n^2)，空间复杂度O(n)

var twoSum = function(nums, target) {    if(nums.length <=1)        return;    for(let i=0;i

solution2:

时间复杂度O(n)，空间复杂度O(n)

var twoSum = function(nums, target) {    if(nums.length <=1)        return;    var hash = {}    for(let i=0;i