Algorithms for Interview 1: Stack

example3.py

class Solution:
    def removeDuplicates(self, S: str) -> str:
        stack = []
        for char in S:
            if (not stack) or (stack[-1]!=char):
                stack.append(char)
            else:
                while stack and stack[-1] == char:
                    stack.pop()
        return ''.join(stack)