394. 字符串解码 - 力扣（LeetCode）

class Solution:
    def decodeString(self, s: str) -> str:
        stack = []
        num = 0
        curr_str = ""
        
        for char in s:
            if char.isdigit():
                num = num * 10 + int(char)
            elif char == '[':
                stack.append((curr_str, num))
                curr_str, num = "", 0
            elif char == ']':
                last_str, repeat = stack.pop()
                curr_str = last_str + curr_str * repeat
            else:
                curr_str += char
        
        return curr_str