61 lines
1.8 KiB
Nix
61 lines
1.8 KiB
Nix
# nix eval -f ./day_1.nix part1
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# nix eval -f ./day_1.nix part1 --arg input 'builtins.readFile ./puzzle_cache/day_1_1'
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# nix eval -f ./day_1.nix part2
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# nix eval -f ./day_1.nix part2 --arg input 'builtins.readFile ./puzzle_cache/day_1_1'
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{
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input ? (builtins.readFile ./puzzle_cache/day_1_0),
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}:
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with builtins;
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with import ./utils.nix;
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let
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# Split into non-empty lines
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lines = builtins.filter (s: builtins.isString s && s != "") (builtins.split "\n" input);
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# Parse a line like "L68" or "R14"
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parseLine = line: {
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dir = builtins.substring 0 1 line;
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dist = toIntBase10 (builtins.substring 1 (builtins.stringLength line - 1) line);
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};
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rotations = map parseLine lines;
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countZerosDuring =
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position: dir: dist:
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if dir == "R" then
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floor ((position + dist) / 100.0) - floor (position / 100.0)
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else if dir == "L" then
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floor ((position -1) / 100.0) - floor ((position - dist - 1) / 100.0)
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else
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builtins.throw "Invalid direction: ${dir}";
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# Fold over the list to simulate the dial
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step =
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state: rot:
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let
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position =
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if rot.dir == "L" then
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mod (state.position - rot.dist) 100
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else if rot.dir == "R" then
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mod (state.position + rot.dist) 100
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else
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builtins.trace "Invalid direction: ${rot.dir}" state.position;
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countZeroPassed = state.countZeroPassed + (countZerosDuring state.position rot.dir rot.dist);
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countZero = state.countZero + (if position == 0 then 1 else 0);
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in
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{
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inherit position countZero countZeroPassed;
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};
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initialState = {
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position = 50;
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countZero = 0;
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countZeroPassed = 0;
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};
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finalState = builtins.foldl' step initialState rotations;
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in
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{
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part1 = finalState.countZero;
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part2 = finalState.countZeroPassed;
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# 6689 should be part 2
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}
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