leetcode1047

class Solution:
    def removeDuplicates(self, S: str) -> str:
        l = []
        for i in range(len(S)):
            s = S[i]
            if len(l) == 0:
                l.append(s)
            else:
                top = l[-1]
                if s == top:
                    l.pop(-1)
                else:
                    l.append(s)
        result = ''
        for i in range(len(l)):
            result += l[i]
        return result