1209-remove-all-adjacent-duplicates-in-string-ii.py

class Solution:
    def removeDuplicates(self, s: str, k: int) -> str:
        stack = []  # [char, count]

        for c in s:
            if stack and stack[-1][0] == c:
                stack[-1][1] += 1
            else:
                stack.append([c, 1])

            if stack[-1][1] == k:
                stack.pop()

        res = ""
        for char, count in stack:
            res += char * count

        return res