Runtime: 109 ms , Your runtime beats 4.36 % of cpp submissions.

561_Array Partition.cpp

#include <algorithm>
class Solution {
public:
    int arrayPairSum(vector<int>& nums) {
    vector<int>::size_type sz = nums.size();
       sort(nums.begin(),nums.end());
       int total = 0;
      for(int i=0;i<sz;i+=2)
      {
         total+=nums[i];
      }
      return total;
    }
};