class Solution:
    def decodeString(self, s_: str) -> str:
        s = []
        for c in s_:
            if c == "[":
                s.append(Solution)
            elif c == "]":
                ts = s.pop()
                s.pop()
                tn = s.pop()
                s.append(ts * tn)
            elif "0" <= c <= "9":
                if s and isinstance(s[-1], int):
                    s[-1] *= 10
                    s[-1] += int(c)
                else:
                    s.append(int(c))
            else:
                s.append(c)


            while (
                len(s) > 1 and
                isinstance(s[-1], str) and
                isinstance(s[-2], str)
            ):
                t = s[-2] + s[-1]
                s.pop()
                s.pop()
                s.append(t)

        return s[0]