RLE Decompress/ compress

def compress(input_string):
    if not input_string:
        return ""
    
    compressed = []
    count = 1
    length = len(input_string)

    for i in range(1, length):
        if input_string[i] == input_string[i - 1]:
            count += 1
        else:
            compressed.append(input_string[i - 1] + str(count))
            count = 1

    # Append the last character and its count
    compressed.append(input_string[-1] + str(count))
    
    return ''.join(compressed)

def decompress(compressed_string):
    if not compressed_string:
        return ""
    
    decompressed = []
    i = 0
    length = len(compressed_string)

    while i < length:
        char = compressed_string[i]
        i += 1
        
        # Check if the next character(s) are digits
        count_str = ''
        while i < length and compressed_string[i].isdigit():
            count_str += compressed_string[i]
            i += 1
        
        if not count_str:
            return "Invalid format: Missing count after character."
        
        count = int(count_str)
        decompressed.append(char * count)

    return ''.join(decompressed)

if __name__ == "__main__":
    while True:
        print("\nRun-Length Encoding (RLE) Compression and Decompression")
        print("1. Compress a string")
        print("2. Decompress a string")
        print("3. Exit")
        
        choice = input("Choose an option (1/2/3): ")
        
        if choice == '1':
            input_string = input("Enter the string to compress: ")
            compressed_string = compress(input_string)
            print(f"Compressed: {compressed_string}")
        
        elif choice == '2':
            compressed_string = input("Enter the RLE-compressed string to decompress: ")
            decompressed_string = decompress(compressed_string)
            print(f"Decompressed: {decompressed_string}")
        
        elif choice == '3':
            print("Exiting the program.")
            break
        
        else:
            print("Invalid choice. Please select 1, 2, or 3.")