--- Day 1: Calorie Counting --- Sum it up!
--- Day 2: Rock Paper Scissors --- Simulate RPS game.
--- Day 3: Rucksack Reorganization --- Find common characters.
--- Day 4: Camp Cleanup --- Ranges.
--- Day 5: Supply Stacks --- Stacks.
--- Day 6: Tuning Trouble --- Slice
--- Day 7: No Space Left On Device --- A good old tree. Sort of. (just added each file size to all ancestors)
--- Day 8: Treetop Tree House --- Counting on a grid!
--- Day 9: Rope Bridge --- Rope simulation! Alt snake.
--- Day 10: Cathode-Ray Tube --- Simulate the "addx", "noop" cycles to generate an image.
--- Day 11: Monkey in the Middle --- Some number theory.
--- Day 12: Hill Climbing Algorithm --- Pathfinding.
--- Day 13: Distress Signal --- Recursive array sorting.
--- Day 14: Regolith Reservoir --- Sand flow.
--- Day 15: Beacon Exclusion Zone --- Manhattan distance.
--- Day 16: Proboscidea Volcanium --- Valves and pipes.
--- Day 17: Pyroclastic Flow --- Tetris!
--- Day 18: Boiling Boulders --- 3d flood fill
--- Day 19: Not Enough Minerals --- Operations planning
--- Day 20: Grove Positioning System --- Circular list
--- Day 21: Monkey Math --- Recursive operations
--- Day 22: Monkey Map --- Cube map!
--- Day 23: Unstable Diffusion --- Diffusion algorithm
--- Day 24: Blizzard Basin --- Path finding.
--- Day 25: Full of Hot Air ---