LeetCode-in-Java

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

public class Solution {
    public int maxValidPairSum(int[] nums, int k) {
        int res = 0;
        int pre = 0;
        int n = nums.length;
        for (int i = 0; i < n - k; i++) {
            pre = Math.max(pre, nums[i]);
            res = Math.max(res, pre + nums[i + k]);
        }
        return res;
    }
}

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