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:

1. n is a positive integer, which is in the range of [1, 10000].
2. All the integers in the array will be in the range of [-10000, 10000].

int arrayPairSum(vector<int>& nums) {
        sort(nums.begin(),nums.end());
        int res=0;
        for(int i=0;i<nums.size();)
        {
            res=res+nums[i];
            i+=2;
        }
        return res;
    }

（leetcode题解）Array Partition I