561. Array Partition I

package LeetCode_561

/**
 * 561. Array Partition I
 * https://leetcode.com/problems/array-partition-i/
 * 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.
 * */
class Solution {
    /*
    * solution: greedy, sort array, set two number as a group then sum up every group‘s first num,
    * Time:O(nlogn), Space:O(1)
    * */
    fun arrayPairSum(nums: IntArray): Int {
        nums.sort()
        var result = 0
        for (i in nums.indices step 2) {
            result += nums[i]
        }
        return result
    }
}