0561 - Array Partition I

## Description of the Problem
First, given array is sorted. And the sum was obtained by increasing the index of the array by two. That is sum of min(ai, bi) at problem.

## Code
```
class Solution:
    def arrayPairSum(self, nums: List[int]) -> int:
        return sum(sorted(nums)[::2])
```

## Link To The LeetCode Problem
[LeetCode](https://leetcode.com/problems/array-partition-i/)
