Solution to Leetcode 394 Decode String

soln_lc394.py

class Solution:
    def decodeString(self, s: str) -> str:
        stack = []

        for i in s:
            if i != "]":
                stack.append(i)
            else:
                substring = ""
                while stack[-1] != "[":
                    substring = stack.pop() + substring
                # pop "["
                stack.pop()

                k = ""
                while stack and stack[-1].isdigit():
                    k = stack.pop() + k
                stack.append(int(k) * substring)
        
        return "".join(stack)