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@gnyman
Created December 6, 2022 13:34
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# Parse the input
data = open('input.txt').read().strip()
# Keep track of the last four characters received
last_four = []
last_fourteen = []
# Keep track of whether the start-of-packet marker and the
# start-of-message marker have been found
packet_marker_found = False
message_marker_found = False
# Process each character in the data
for i, ch in enumerate(data):
# Add the character to the list of last four characters
last_four.append(ch)
last_fourteen.append(ch)
# If we have more than four characters, remove the first one
if len(last_four) > 4:
last_four.pop(0)
if len(last_fourteen) > 14:
last_fourteen.pop(0)
# If the last four characters are all different and we haven't
# already found the start-of-packet marker, we have found
# a start-of-packet marker, so print the number of characters
# processed and mark that we have found it
if len(set(last_four)) == 4 and not packet_marker_found:
print(f"First start-of-packet marker after {i+1} characters")
packet_marker_found = True
# If the last 14 characters are all different and we haven't
# already found the start-of-message marker, we have found
# a start-of-message marker, so print the number of characters
# processed and mark that we have found it
if len(set(last_fourteen)) == 14 and not message_marker_found:
print(f"First start-of-message marker after {i+1} characters")
message_marker_found = True
# If we have found both markers, stop processing the input
if packet_marker_found and message_marker_found:
break
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