Given an array of2nintegers, your task is to group these integers intonpairs 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].

所以这个教诲了我们什么呢？大概就是sort的用法把。。。