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 = min(1, 2) + min(3, 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].

class Solution {
    public int arrayPairSum(int[] nums) {
        int res = 0;
        int n = nums.length / 2;
        Arrays.sort(nums);
        for(int i = 0; i < nums.length; i++){
            if(i % 2 == 0) res += nums[i];
        }
        return res;
    }
}

??

https://leetcode.com/problems/array-partition-i/discuss/102170/Java-Solution-Sorting.-And-rough-proof-of-algorithm.

 https://www.cnblogs.com/jimmycheng/p/7119306.html