Decryption

Message from Space

Challenge Difficulty: Medium | Estimated completion time: ~30 minutes

You have received an encrypted message from space. Your task is to decrypt the message with the following simple rules:

• Message string will consist of capital letters, numbers, and brackets only.
• When there’s a block of code inside the brackets, such as [10AB], it means you need to repeat the letters AB for 10 times.
• Message can be embedded in multiple layers of blocks.
• Final decrypted message will only consist of capital letters.

Create a function that takes encrypted message str and returns the decrypted message.

Examples

spaceMessage("ABCD")
output = "ABCD"
 
spaceMessage("AB[3CD]")
output = "ABCDCDCD"
# "AB" = "AB"
# "[3CD]" = "CDCDCD"
# Combine both = "ABCDCDCD"
 
spaceMessage("IF[2E]LG[5O]D")
output = "IFEELGOOOOOD"

Solution

Python

def space_message(message: str) -> str: """Decrypt a message with bracketed repetition patterns. Args: message: Encrypted message with patterns like [3AB] Returns: Decrypted message """ stack: list[str] = [] current_string = "" current_number = "" for char in message: if char.isdigit(): current_number += char elif char == "[": stack.append(current_string) stack.append(current_number) current_string = "" current_number = "" elif char == "]": repeat_count = int(stack.pop()) previous_string = stack.pop() current_string = previous_string + current_string * repeat_count else: current_string += char return current_string if __name__ == "__main__": print(space_message("ABCD")) # ABCD print(space_message("AB[3CD]")) # ABCDCDCD print(space_message("IF[2E]LG[5O]D")) # IFEELGOOOOOD

Output