I am trying to solve 394. Decode String on Leetcode, this was my solution (I know it’s inefficient):

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

        for ch in s:
            if ch != ']':
                stack.append(ch)
            else:
                new_s = ''
                while stack[-1] != '[':
                    new_s += stack.pop()
                new_s = new_s[::-1]
                stack.pop()

                number = ''
                while stack and stack[-1].isdigit():
                    print(stack[-1])
                    number += stack.pop()
                number = int(number[::-1])

                
                print(new_s)
                stack.append(number * new_s)
        
        return "".join(stack) 

and this is the working solution:

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

        for ch in s:
            if ch != ']':
                stack.append(ch)
            else:
                # Collect the characters forming the encoded string
                decoded_string = []
                while stack[-1] != '[':
                    decoded_string.append(stack.pop())
                stack.pop()  # Remove the '['
                
                # Now reverse the decoded string to get the correct order
                decoded_string = ''.join(decoded_string[::-1])
                
                # Get the number (how many times to repeat)
                number = []
                while stack and stack[-1].isdigit():
                    number.append(stack.pop())
                number = int(''.join(number[::-1]))

                # Append the repeated decoded string back to the stack
                stack.append(number * decoded_string)
        
        return "".join(stack)

Why is the first function not working? I really think that there is no difference except that I am reversing a string, and the correct code reverses the list.

Idk what to say here except that I just don’t see why one algo works and the other doesn’t…