Given an array of 2n integers, your task is to group these integers into n pairs of integer,

say (a1, b1), (a2, b2), ..., (an, bn) which makes sum of min(ai, bi) for all i from 1 to n as large as possible.

Example 1:

Input: [1,4,3,2]

Output: 4

Explanation: n is 2, and the maximum sum of pairs is 4.

Note:

n is a positive integer, which is in the range of [1, 10000].

All the integers in the array will be in the range of [-10000, 10000].

思路：

先从小到大排序，然后取每一个pair的第一个值相加即可，至于为什么这么做。。还没想清楚。

int arrayPairSum(vector
     
      & nums){    int result = 0;        sort(nums.begin(),nums.end());    for(int i =0;i