561. Array Partition I （easy）

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).

這道題提意不清，其實是要求把一個2n的array兩兩一組，將每組的最小值相加，問如何得到的和最大，

即sum（all min（xi，xj）） 

萬能排序，然後按2個一組，min就是下標為偶數的數

class Solution:
    def arrayPairSum(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        nums.sort()
        return sum([nums[i] for i in range(len(nums)) if i%2==0 ])
 

Runtime: 124 ms, faster than 62.36% of Python3