def decode_string(encoded: str) -> str: stack: list = [] current_num: str = '' current_str: str = '' for char in encoded: if char.isdigit(): current_num = current_num * 10 + int(char) elif char == '[': stack.append((current_str, current_num)) current_str = '' current_num = 0 elif char == ']': prev_str, repeat_num = stack.pop() current_str = prev_str + current_str * repeat_num else: current_str += char return current_str input_string = '3[a]2[bc]' print(decode_string(input_string))

Output: aaabcbc

Explanation: The input string "3[a]2[bc]" can be decoded as "aaa" + "bc" + "bc" = "aaabcbc"