Remove All Adjacent Duplicates in String II — LeetCode 1209 Python Solution

The problem

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.

Example

Input

s = "abcd", k = 2

Output

"abcd"

Explanation

There's nothing to delete.

Python solution

class Solution:
    def removeDuplicates(self, s: str, k: int) -> str:
        stk = []
        for c in s:
            if stk and stk[-1][0] == c:
                stk[-1][1] = (stk[-1][1] + 1) % k
                if stk[-1][1] == 0:
                    stk.pop()
            else:
                stk.append([c, 1])
        ans = [c * v for c, v in stk]
        return "".join(ans)

Complexity

Pattern: Stack

When the most recent unresolved thing is the one that matters, use a stack. LeetCode 1209. Remove All Adjacent Duplicates in String II is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Stack.

The stack guide has the Python template for the pattern and the 194 LeetCode problems that use it.

Related problems