Given an array of integers, find two numbers such that they add up to a specific target number.

The function twoSum should return indices of the two numbers such that they add up to the target, where index1 must be less than index2. Please note that your returned answers (both index1 and index2) are not zero-based.

You may assume that each input would have exactly one solution.

Input: numbers={2, 7, 11, 15}, target=9

Output: index1=1, index2=2

题意：给出无序数组A，找出两数之和等于目标数target

1.使用哈希表

2.转换思维，由两数之和转换成目标数与当前遍历数字的差

代码如下：

1 public class Solution { 2     public int[] twoSum(int[] nums, int target) { 3        Map
     
       map = new HashMap
      
       (); 4         int[] rs = new int[2]; 5         for (int i = 0; i < nums.length; ++i) { 6             int tmp = target - nums[i]; 7             if (map.get(tmp) == null) { 8                 map.put(nums[i], i + 1); 9             }10             else {11                 rs[0] = map.get(tmp);12                 rs[1] = i + 1;13                 break;14             }15         }16 17         return rs;18     }19 }