commitdd92cf0f8f1931a0e1d5af4203fffd02efec3cd5parent993f9555566d97b99f9853aa741fb62f494dc9a1Author:Eamon Caddigan <eamon.caddigan@gmail.com>Date:Wed, 8 Dec 2021 20:31:39 -0500 Solution to day 8, part 2, plus fixed a mistake in my commentsDiffstat:

M | day08_part1.py | | | 6 | ++++-- |

A | day08_part2.py | | | 137 | +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ |

M | utils.py | | | 5 | +++++ |

3 files changed, 146 insertions(+), 2 deletions(-)diff --git a/day08_part1.py b/day08_part1.py@@ -20,8 +20,8 @@ displays""" # '3' and '4', that's '9' # * If 6 segments are lit and it's not a '6' or '9', that's '0' # * If 5 segments are lit and it is missing only one of the segments from '6', -# that's '2' -# * If 5 segments are lit and it's not a '2' or a '3', that's '5' +# that's '5' +# * If 5 segments are lit and it's not a '5' or a '3', that's '2' # So right now in part 1, it's possible to find the four digits displayed for # each line of puzzle input! But... # I'm not going to implement it yet, because "good programmers are lazy", and @@ -58,6 +58,8 @@ def convert_input_to_df(input_string): .str.rsplit(' ', 4, expand=True) .rename(columns=dict(enumerate(('segments', 'digit_1', 'digit_2', 'digit_3', 'digit_4')))) + .assign(segments=lambda x: x['segments'].str.replace(' |', '', + regex=False)) ) display_df.loc[:, 'digit_1':'digit_4'] = ( display_df.loc[:, 'digit_1':'digit_4'].applymap(frozenset)diff --git a/day08_part2.py b/day08_part2.py@@ -0,0 +1,137 @@ +#!/usr/bin/env python +"""Advent of Code 2021, day 8 (part 2): decode all of the scrambled +seven-segment displays""" + +# This is a fun puzzle. I sat down with pen and paper and proved to myself that +# you can deduce the mapping from scrambled segments to the full set of digits +# using just the information provided. It looks like this: +# * If 2 segments are lit, that's '1' +# * If 3 segments are lit, that's '7' +# * If 4 segments are lit, that's '4' +# * If 7 segments are lit, that's '8' +# (So far, this was given in the puzzle prompt, nothing new yet) +# * If 5 segments are lit, it's '2', '3', or '5' +# * If 6 segments are lit, it's '0', '6', or '9' +# (Okay, that's not useful... yet) +# * If 5 segments are lit and they include all the segments in '7', that's '3' +# * If 6 segments are lit and they don't include all the segments in '7', +# that's '6' +# * If 6 segments are lit and they include the union of the segments comprising +# '3' and '4', that's '9' +# * If 6 segments are lit and it's not a '6' or '9', that's '0' +# * If 5 segments are lit and it is missing only one of the segments from '6', +# that's '5' +# * If 5 segments are lit and it's not a '2' or a '3', that's '2' +# So right now in part 1, it's possible to find the four digits displayed for +# each line of puzzle input! But... +# I'm not going to implement it yet, because "good programmers are lazy", and +# maybe part 2 will throw me for a loop? Regardless, figuring this out has +# influenced my decision about how to represent the data; e.g., we're doing a +# lot of set operations, so I'm going to use sets for everything, and since +# it's easy to imagine wanting to use these sets of lit segments as dictionary +# keys, we'll use immutable `frozenset`s specifically (which can be `dict` +# keys). + + +from day08_part1 import (EXAMPLE_INPUT, + convert_input_to_df, + apply_mappers_to_digits) +from utils import get_puzzle_input + +def create_mapper_from_segments(segment_sequence): + """Given the observed sequence of segment sets (which isn't actually used + for anything here), return a function that maps a `frozenset` of segments + to a digit""" + + # This approach isn't efficient (or elegant) at all, but I don't think this + # function is being run enough times, on a long enough list, to justify the + # code complexity for a more efficient/elegant approach + segment_sets = [frozenset(i) for i in segment_sequence.split(' ')] + digits_to_segments = {} + + # Step 1 of building a segment to digit map: find the mapping to '1', '7', + # '4', and '8' + for i, seg in enumerate(segment_sets): + if len(seg) == 2: + digits_to_segments['1'] = segment_sets.pop(i) + break + for i, seg in enumerate(segment_sets): + if len(seg) == 3: + digits_to_segments['7'] = segment_sets.pop(i) + break + for i, seg in enumerate(segment_sets): + if len(seg) == 4: + digits_to_segments['4'] = segment_sets.pop(i) + break + for i, seg in enumerate(segment_sets): + if len(seg) == 7: + digits_to_segments['8'] = segment_sets.pop(i) + break + + # Step 2: using '7' alone, find '3' and '6' + for i, seg in enumerate(segment_sets): + if len(seg) == 5 and not digits_to_segments['7'] - seg: + digits_to_segments['3'] = segment_sets.pop(i) + break + for i, seg in enumerate(segment_sets): + if len(seg) == 6 and (digits_to_segments['7'] - seg): + digits_to_segments['6'] = segment_sets.pop(i) + break + + # Step 3: Using '4', '3', and '6', find '9', and '5' + for i, seg in enumerate(segment_sets): + if len(seg) == 5 and len(digits_to_segments['6'] - seg) == 1: + digits_to_segments['5'] = segment_sets.pop(i) + break + for i, seg in enumerate(segment_sets): + if len(seg) == 6 and \ + seg == digits_to_segments['3'] | digits_to_segments['4']: + digits_to_segments['9'] = segment_sets.pop(i) + break + + # Step 4 (final): Using '3', '6', '2', and '9', find '0' and '2' + for i, seg in enumerate(segment_sets): + if len(seg) == 5: + digits_to_segments['2'] = segment_sets.pop(i) + break + digits_to_segments['0'] = segment_sets.pop() + + segments_to_digits = {v:k for k, v in digits_to_segments.items()} + + def part_2_mapper(segments): + """Just a closure wrapping the dictionary (hackily) built above""" + return segments_to_digits.get(segments) + return part_2_mapper + +def convert_single_digits_to_integers(digits_df): + """Given a four-column df of digit displays, return a Series consisting of + a the single integer value obtained across each row""" + # Can this be done with `apply` somehow? This feels needlessly inelegant + return ( + digits_df['digit_1'] + .add(digits_df['digit_2']) + .add(digits_df['digit_3']) + .add(digits_df['digit_4']) + .astype(int) + ) + +def solve_puzzle(input_string): + """Return the numeric solution to the puzzle""" + return int( + convert_single_digits_to_integers( + apply_mappers_to_digits( + convert_input_to_df(input_string), + create_mapper_from_segments + ) + ) + .sum() + ) + +def main(): + """Run when the file is called as a script""" + assert solve_puzzle(EXAMPLE_INPUT) == 61229 + print("Sum of all decoded displays:", + solve_puzzle(get_puzzle_input(8))) + +if __name__ == "__main__": + main()diff --git a/utils.py b/utils.py@@ -5,6 +5,11 @@ import requests import numpy as np import pandas as pd +def convert_lines_to_series(input_string): + """Return a pandas Series consisting of the lines in the + (newline-delimited) input string""" + return pd.Series(input_string.rstrip('\n').split('\n')) + def convert_int_line_to_series(input_string): """Converts one (optionally newline-terminated) string of comma-separated integers to a pandas Series"""