Remove All Adjacent Duplicates In String II

You are given a string s and an integer k, a k duplicate removal consists of choosing k adjacent and equal letters from s and removing them, causing the left and the right side of the deleted substring to concatenate together.

We repeatedly make k duplicate removals on s until we no longer can.

Return the final string after all such duplicate removals have been made. It is guaranteed that the answer is unique.

Example 1:

Input: s = "abcd", k = 2

Output: "abcd"

Explanation: There's nothing to delete.

Example 2:

Input: s = "deeedbbcccbdaa", k = 3

Output: "aa"

Explanation:
First delete "eee" and "ccc", get "ddbbbdaa"
Then delete "bbb", get "dddaa"
Finally delete "ddd", get "aa"

Example 3:

Input: s = "pbbcggttciiippooaais", k = 2

Output: "ps"

Constraints:

• 1 <= s.length <= 100,000
• 2 <= k <= 10,000
• s only contains lowercase English letters.

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