Two Sum

## Problem：
##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].
```
## Code
```
public class Solution {
    public int[] twoSum(int[] nums, int target) {
        Map map = new HashMap<>();//HashMap查值
        
        for(int i=0;i