3510 - Minimum Pair Removal to Sort Array II.

Hard

Given an array nums, you can perform the following operation any number of times:

• Select the adjacent pair with the minimum sum in nums. If multiple such pairs exist, choose the leftmost one.

• Replace the pair with their sum.

Return the minimum number of operations needed to make the array non-decreasing.

An array is said to be non-decreasing if each element is greater than or equal to its previous element (if it exists).

Example 1:

Input: nums = 5,2,3,1

Output: 2

Explanation:

• The pair (3,1) has the minimum sum of 4. After replacement, nums = [5,2,4].

• The pair (2,4) has the minimum sum of 6. After replacement, nums = [5,6].

The array nums became non-decreasing in two operations.

Example 2:

Input: nums = 1,2,2

Output: 0

Explanation:

The array nums is already sorted.

Constraints:

• <code>1 <= nums.length <= 10⁵</code>

• <code>-10⁹<= numsi<= 10⁹</code>