day6_take5.py

import sys

# Get the filename from the command line argument
filename = sys.argv[1]

# Open the file and read its contents
with open(filename) as f:
    data = f.read()

# Define a function to find the packet start
def find_packet_start(data):
    # Initialize the window of four characters
    window = ["", "", "", ""]

    # Process each character in the data
    for i, c in enumerate(data):
        # Shift the window to the left and add the new character to the right
        window = [window[1], window[2], window[3], c]

        # Check if the four characters in the window are all different
        if len(set(window)) == 4:
            # Return the number of characters processed so far
            return i + 1

# Find the packet start and print the result
result = find_packet_start(data)
print(result)