leetcode练习：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   

刚开始又理解错题目意思了噗，这是要分成两个一组，分成n组，它也正好是2n个数。它要让所有的分组里面的最小数加起来是最大的。

我们会发现如果是这样，就只能按照排序之后，两个两个分组，这样加起来是最大的。

var arrayPairSum = function(nums) {
    var max_num = 0;
    var len = nums.length;
    
    nums.sort(cmp);
    
    for(var i=0;i<len;){
        max_num += nums[i];
        i+=2;
    }
    
    return max_num;
};

function cmp (a,b){
    return a - b;
}