alexander-held / advent-of-code-2020

Code for solutions to the 2020 edition of Advent of Code

Advent of Code 2020

This repository is now superseded by alexander-held/advent-of-code.

Solutions to Advent of Code 2020 puzzles: https://adventofcode.com/2020.

What is each day about?

• 01: finding values summing to specific number in list
• 02: password parsing, applying rules to determine valid passwords
• 03: 2d grid navigation, counting trees hit when taking different paths
• 04: passport parsing, input parsing and rule application
• 05: boarding pass parsing, base-2 math
• 06: customs forms, set unions and intersections
• 07: bags contained inside bags following rules / memoization
• 08: running game console code to calculate number, changing one instruction to make code terminate
• 09: subset of numbers in list that follows rules
• 10: adapter array to charge device, finding all possible configurations / dynamic programming
• 11: 2d cellular automaton: seat assignments
• 12: 2d grid navigation
• 13: coinciding bus departure times, least common multiple with offsets / Chinese remainder theorem
• 14: program with bitmasks
• 15: evaluating n-th number following game where next number depends on history
• 16: matching rules to list of examples following rules in unknown order to determine order of rules in example
• 17: 3d and 4d cellular automata
• 18: expression parsing with custom operator precedence
• 19: counting messages satisfying rules with loops / context-free grammar
• 20: arranging puzzle pieces to solve puzzle, finding sea monster in solved image
• 21: matching allergens to ingredients in list of food items / bipartite matching
• 22: playing 2-player card game with recursion
• 23: circle cup game / linked list
• 24: hexagonal grid navigation / cellular automaton
• 25: finding encryption key of handshake