4066. Maximum Equal Adjacent Pairs After at Most One Replacement - Solution & Explanation

Problem Statement

You are given a 1-indexed integer array nums.

You can choose two distinct values x and y and perform the following operation at most once:

Return the maximum possible number of pairs of adjacent elements that are equal after performing the operation.

Example 1:

Input: nums = [1,2,3,2]

Output: 2

Explanation:

One optimal solution is to choose x = 3 and y = 2.
The resulting array is [1, 2, 2, 2].
There are 2 pairs of adjacent elements that are equal: (nums[2], nums[3]) and (nums[3], nums[4]).
Therefore, the answer is 2.

Example 2:

Input: nums = [1,2,1,2,1]

Output: 4

Explanation:

One optimal solution is to choose x = 1 and y = 2.
The resulting array is [2, 2, 2, 2, 2].
There are 4 pairs of adjacent elements that are equal: (nums[1], nums[2]), (nums[2], nums[3]), (nums[3], nums[4]), and (nums[4], nums[5]).
Therefore, the answer is 4.

Example 3:

Input: nums = [1,1,1]

Output: 2

Explanation:

One optimal solution is to perform no operation.
Thus, the resulting array is [1, 1, 1].
There are 2 pairs of adjacent elements that are equal: (nums[1], nums[2]) and (nums[2], nums[3]).
Therefore, the answer is 2.

Constraints:

Maximum Equal Adjacent Pairs After at Most One Replacement - Solution & Explanation