Solution.py3

class Solution:
    def backspaceCompare(self, S: str, T: str) -> bool:
        def move(s, i):
            while i >= 0 and s[i] == '#':
                c = 0
                while i >= 0 and s[i] == '#':
                    c += 1
                    i -= 1
                while i >= 0 and c > 0:
                    c += 1 if s[i] == '#' else -1
                    i -= 1

            return i

        i, j = len(S) - 1, len(T) - 1
        while i >= 0 or j >= 0:
            i = move(S, i)
            j = move(T, j)
            if i >= 0 and j >= 0:
                if S[i] != T[j]:
                    return False
                i -= 1
                j -= 1
            elif i >= 0 or j >= 0:
                return False

        return i == j