LeetCode in Kotlin

3979. Maximum Valid Pair Sum

Medium

You are given an integer array nums of length n and an integer k.

A pair of indices (i, j) is called valid if:

• 0 <= i < j < n
• j - i >= k

Return the maximum value of nums[i] + nums[j] among all valid pairs.

Example 1:

Input: nums = [1,3,5,2,8], k = 2

Output: 13

Explanation:

The valid pairs are:

• (0, 2): nums[0] + nums[2] = 6
• (0, 3): nums[0] + nums[3] = 3
• (0, 4): nums[0] + nums[4] = 9
• (1, 3): nums[1] + nums[3] = 5
• (1, 4): nums[1] + nums[4] = 11
• (2, 4): nums[2] + nums[4] = 13

Thus, the answer is 13.

Example 2:

Input: nums = [5,1,9], k = 1

Output: 14

Explanation:

• Since k = 1, every pair is valid.
• The maximum value is obtained from a pair (0, 2), which is nums[0] + nums[2] = 5 + 9 = 14.
• Thus, the answer is 14.

Constraints:

• 2 <= n == nums.length <= 105
• 1 <= nums[i] <= 109
• 1 <= k <= n - 1

Solution

import kotlin.math.max

class Solution {
    fun maxValidPairSum(nums: IntArray, k: Int): Int {
        var res = 0
        var pre = 0
        val n = nums.size
        for (i in 0..<n - k) {
            pre = max(pre, nums[i])
            res = max(res, pre + nums[i + k])
        }
        return res
    }
}

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