These are my solutions to Advent of Code 2023 for years 2022, 2023, 2024 (ongoing). They are all coded in Java, needing Java 21 at least.

Index

2022

• 2022-12-01: solution (maximum sums of numbers).
• 2022-12-02: solution (rock paper scissors).
• 2022-12-03: solution (finding items common to sets).
• 2022-12-04: solution (overlaps between number ranges).
• 2022-12-05: solution (moving crates between stacks).
• 2022-12-06: solution (first occurrence of n distinct characters in a string).
• 2022-12-07: solution (directory hierarchy sizes from command outputs).
• 2022-12-08: solution (visibility from trees in a forest).
• 2022-12-09: solution (maintaining minimum distances in a rope as it moves).
• 2022-12-10: solution (simulating a CPU drawing pixels on a CRT).
• 2022-12-11: solution (monkeys throwing items based on arithmetic operations).
• 2022-12-12: solution (shortest path climbing).
• 2022-12-13: solution (comparing nested lists).
• 2022-12-14: solution (falling sand forming piles).
• 2022-12-15: solution (beacons and sensors with Manhattan distances).
• 2022-12-16: solution (opening valves and traversing tunnels).
• 2022-12-17: solution (falling rocks and gas jets).
• 2022-12-18: solution (exposed surface area of cubes).
• 2022-12-19: solution (choosing between cost sets for building robots).
• 2022-12-20: solution (moving numbers in a cyclic list).
• 2022-12-21: solution (solving an equation expressed as a tree).
• 2022-12-22: solution (following paths on the surface of a cube).
• 2022-12-23: solution (fixed point of cellular automaton).
• 2022-12-24: solution (path through a grid with shifting obstacles).
• 2022-12-25: solution (base 5 numbers using digits -2..2).

2023

• 2023-12-01: solution (extracting integers from strings).
• 2023-12-02: solution (possible draws from a bag of coloured cubes).
• 2023-12-03: solution (extracting integers from a grid with adjacent characters).
• 2023-12-04: solution (evaluating scratch cards).
• 2023-12-05: solution (tracing number ranges through a sequence of maps).
• 2023-12-06: solution (timing races).
• 2023-12-07: solution (evaluating poker hands).
• 2023-12-08: solution (sequences of left-right choices through a graph).
• 2023-12-09: solution (successive differences).
• 2023-12-10: solution (length and enclosed area of a path).
• 2023-12-11: solution (cosmic expansion).
• 2023-12-12: solution (matching wildcards against counts).
• 2023-12-13: solution (searching for reflections).
• 2023-12-14: solution (cycles of rolling rocks).
• 2023-12-15: solution (hashing).
• 2023-12-16: solution (tracing a beam with splitting).
• 2023-12-17: solution (least-cost path with constraints).
• 2023-12-18: solution (area enclosed by a path).
• 2023-12-19: solution (DFA with conditions on 4 variables).
• 2023-12-20: solution (cycling behaviour of circuits).
• 2023-12-21: solution (counting paths in a graph).
• 2023-12-22: solution (3D bricks falling vertically).
• 2023-12-23: solution (longest path through a graph).
• 2023-12-24: solution (intersections of 3D lines).
• 2023-12-25: solution (finding a 3-cut in a large graph).

2024

• 2024-12-01: solution (pairing up integers from two lists).
• 2024-12-02: solution (checking adjacent deltas in lists of numbers).
• 2024-12-03: solution (extracting instructions from a string including junk).
• 2024-12-04: solution (word-search XMAS).
• 2024-12-05: solution (sorting number lists based on pairwise orders).
• 2024-12-06: solution (paths in a grid with obstacles).
• 2024-12-07: solution (making equations true by inserting operators).
• 2024-12-08: solution (points aligned with pairs of points in a grid).
• 2024-12-09: solution (disk compaction).
• 2024-12-10: solution (counting paths in a graph).
• 2024-12-11: solution (exponential evolution of a list of numbers).
• 2024-12-12: solution (perimeters and side counts of regions in a grid).
• 2024-12-13: solution (simultaneous Diophantine equations).
• 2024-12-14: solution (vector-moving robots forming a Christmas tree).
• 2024-12-16: solution (shortest path through a maze with penalty for turns).
• 2024-12-17: solution (quining a program on a 3-bit CPU).
• 2024-12-18: solution (shortest path through grid with obstacles).

Acknowledgements

All solutions are entirely the work of Éamonn McManus except as noted below.

• 2022-12-16 (opening valves and traversing tunnels).

  My original solution was very inefficient and I was able to make it much faster using an idea from Martijn Pieters (zopatista) on [Reddit] (https://www.reddit.com/r/adventofcode/comments/zo21au/2022_day_16_approaches_and_pitfalls_discussion/).

• 2023-12-17 (least-cost path with constraints on moves)

  I gave up before finding the right Dynamic Programming approach. I ended up copying my approach from David Brownman.

• 2023-12-20 (pulse propagation)

  I had a strong suspicion of what the right approach might be for Part 2 but would have needed to investigate in detail to confirm. Instead I looked online and found this description by Dazbo, which confirmed my suspicion. Then solving was straightforward.

• 2023-12-21 (counting paths in an infinite graph)

  I was not really motivated to put in the work for Part 2 so I outright cheated, by copying this solution by Michiel Graat.

• 2023-12-24 (intersections of 3-dimensional lines)

  This curious puzzle was entirely solvable with algebra, the computer only serving to solve simultaneous equations. I did the first part myself, but did not find the right approach for the second part on my own. The excellent explanation and solution by @dirk527 showed me the right path, but then there wasn't much for me to write.