561.ArrayPairSum.cs

// 561. Array Partition
// Given an integer array nums of 2n integers, group these integers into n pairs (a1, b1), (a2, b2), ..., (an, bn) 
// such that the sum of min(ai, bi) for all i is maximized. Return the maximized sum.

// Example 1:

// Input: nums = [1,4,3,2]
// Output: 4
// Explanation: All possible pairings (ignoring the ordering of elements) are:
// 1. (1, 4), (2, 3) -> min(1, 4) + min(2, 3) = 1 + 2 = 3
// 2. (1, 3), (2, 4) -> min(1, 3) + min(2, 4) = 1 + 2 = 3
// 3. (1, 2), (3, 4) -> min(1, 2) + min(3, 4) = 1 + 3 = 4
// So the maximum possible sum is 4.
// Example 2:
// Input: nums = [6,2,6,5,1,2]
// Output: 9
// Explanation: The optimal pairing is (2, 1), (2, 5), (6, 6). min(2, 1) + min(2, 5) + min(6, 6) = 1 + 2 + 6 = 9.

// Constraints:
// 1 <= n <= 104
// nums.length == 2 * n
// -104 <= nums[i] <= 104

public class Solution {
    public int ArrayPairSum(int[] nums) {
        Array.Sort(nums);
        int sum = 0;
        for(int i = 0; i < nums.Length; i+=2){
            sum += nums[i];
        }
        return sum;
    }
}