[leetcode-561-Array Partition I]

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