1209. Remove All Adjacent Duplicates in String II

Problem Link

Description

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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 <= 105
• 2 <= k <= 104
• s only contains lowercase English letters.

Solution

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Python3

class Solution:
    def removeDuplicates(self, s: str, k: int) -> str:
        stack = []
        
        for x in s:
            if stack and stack[-1][0] == x:
                _, cnt = stack.pop()
                stack.append((x, cnt + 1))
            else:
                stack.append((x, 1))
            
            if stack and stack[-1][1] == k:
                stack.pop()
            
        return "".join(x * cnt for x, cnt in stack)