commit 2f5abb067605f772dcab196ce4802d6948096cc5 · dunkirk.sh/aoc-2025

+177

nix/07/solution.nix

···

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       let

     

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         input = builtins.readFile ../../shared/07/input.txt;

     

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         lines = builtins.filter (s: builtins.isString s && s != "") (builtins.split "\n" input);

     

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       +
         

     

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         # Parse grid into 2D array of characters

     

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         grid = builtins.map (line: builtins.genList (i: builtins.substring i 1 line) (builtins.stringLength line)) lines;

     

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       +
         

     

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         rows = builtins.length grid;

     

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         cols = builtins.length (builtins.head grid);

     

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       +
         

     

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         # Find starting position

     

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         findStart = grid:

     

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           let

     

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             findInRow = rowIdx: row:

     

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               let

     

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                 colIdx = builtins.foldl' (acc: i:

     

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                   if acc != null then acc

     

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                   else if builtins.elemAt row i == "S" then i

     

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                   else null

     

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                 ) null (builtins.genList (i: i) (builtins.length row));

     

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               in if colIdx != null then { r = rowIdx; c = colIdx; } else null;

     

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       +
             

     

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             result = builtins.foldl' (acc: i:

     

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               if acc != null then acc

     

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               else findInRow i (builtins.elemAt grid i)

     

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             ) null (builtins.genList (i: i) (builtins.length grid));

     

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           in result;

     

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       +
         

     

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         startPos = findStart grid;

     

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       +
         

     

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         # Check if position is in bounds

     

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         inBounds = r: c: r >= 0 && r < rows && c >= 0 && c < cols;

     

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         # Get cell at position

     

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         getCell = r: c: 

     

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           if inBounds r c 

     

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           then builtins.elemAt (builtins.elemAt grid r) c

     

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           else ".";

     

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       +
         

     

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         # Part 1: Count total splits

     

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         part1 =

     

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           let

     

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             # Process one step of beams

     

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             stepBeams = state:

     

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               let

     

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                 beams = state.beams;

     

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                 nextBeams = builtins.concatMap (beam:

     

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                   let

     

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                     r = beam.r;

     

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                     c = beam.c;

     

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                     nr = r + 1;

     

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                     nc = c;

     

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                   in

     

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                     if !inBounds nr nc then []

     

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                     else

     

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                       let cell = getCell nr nc;

     

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                       in

     

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                         if cell == "." || cell == "S" then [{ r = nr; c = nc; }]

     

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                         else if cell == "^" then

     

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                           # Split into left and right

     

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                           let

     

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                             left = if inBounds nr (nc - 1) then [{ r = nr; c = nc - 1; }] else [];

     

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                             right = if inBounds nr (nc + 1) then [{ r = nr; c = nc + 1; }] else [];

     

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                           in left ++ right

     

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                         else [{ r = nr; c = nc; }]

     

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                 ) beams;

     

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                 # Count splits in this step

     

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                 splits = builtins.foldl' (acc: beam:

     

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                   let

     

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                     r = beam.r;

     

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                     c = beam.c;

     

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                     nr = r + 1;

     

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                     nc = c;

     

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                     cell = if inBounds nr nc then getCell nr nc else ".";

     

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                   in if cell == "^" then acc + 1 else acc

     

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                 ) 0 beams;

     

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       +
                 

     

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                 # Remove duplicates using string keys

     

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                 uniqueBeams = 

     

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                   let

     

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                     keysSet = builtins.foldl' (acc: beam:

     

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                       acc // { "${toString beam.r},${toString beam.c}" = beam; }

     

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                     ) {} nextBeams;

     

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                   in builtins.attrValues keysSet;

     

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               in

     

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                 {

     

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                   beams = uniqueBeams;

     

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                   totalSplits = state.totalSplits + splits;

     

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                 };

     

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       +
             

     

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             # Run simulation until no beams left

     

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             simulate = state:

     

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               if builtins.length state.beams == 0 

     

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               then state.totalSplits

     

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               else simulate (stepBeams state);

     

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       +
             

     

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             initialState = {

     

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               beams = [{ r = startPos.r; c = startPos.c; }];

     

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               totalSplits = 0;

     

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             };

     

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           in simulate initialState;

     

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       +
         

     

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         # Part 2: Count total timelines

     

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         part2 =

     

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           let

     

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             # Helper to parse "r,c" key

     

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             parseKey = key:

     

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               let

     

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                 parts = builtins.match "([0-9]+),([0-9]+)" key;

     

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               in {

     

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                 r = builtins.fromJSON (builtins.head parts);

     

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                 c = builtins.fromJSON (builtins.elemAt parts 1);

     

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               };

     

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       +
             

     

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             # Process one step with timeline counts

     

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             stepTimelines = states:

     

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               let

     

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                 # For each position with count, move forward

     

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                 nextStates = builtins.foldl' (acc: key:

     

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                   let

     

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                     count = builtins.getAttr key states;

     

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                     pos = parseKey key;

     

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                     r = pos.r;

     

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                     c = pos.c;

     

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                     nr = r + 1;

     

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                     nc = c;

     

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                   in

     

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                     if !inBounds nr nc then acc

     

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                     else

     

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                       let cell = getCell nr nc;

     

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                       in

     

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                         if cell == "." || cell == "S" then

     

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                           # Continue straight

     

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                           let nkey = "${toString nr},${toString nc}";

     

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                           in acc // { ${nkey} = (acc.${nkey} or 0) + count; }

     

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                         else if cell == "^" then

     

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                           # Split into two timelines

     

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                           let

     

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                             left = if inBounds nr (nc - 1) then

     

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                               let lkey = "${toString nr},${toString (nc - 1)}";

     

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                               in { ${lkey} = (acc.${lkey} or 0) + count; }

     

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                             else {};

     

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                             right = if inBounds nr (nc + 1) then

     

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                               let rkey = "${toString nr},${toString (nc + 1)}";

     

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                               in { ${rkey} = (acc.${rkey} or 0) + count; }

     

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                             else {};

     

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                           in acc // left // right

     

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                         else

     

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                           # Continue straight

     

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                           let nkey = "${toString nr},${toString nc}";

     

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                           in acc // { ${nkey} = (acc.${nkey} or 0) + count; }

     

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                 ) {} (builtins.attrNames states);

     

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               in nextStates;

     

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       +
             

     

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             # Run simulation for all rows

     

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             simulate = states: step:

     

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               let

     

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                 nextStates = if step >= rows then {} else stepTimelines states;

     

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                 hasStates = builtins.length (builtins.attrNames nextStates) > 0;

     

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               in

     

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                 if step >= rows || !hasStates

     

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                 then states  # Return last valid states

     

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                 else simulate nextStates (step + 1);

     

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       +
             

     

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             initialStates = { "${toString startPos.r},${toString startPos.c}" = 1; };

     

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             finalStates = simulate initialStates 0;

     

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       +
             

     

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             # Sum all timeline counts

     

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             totalTimelines = builtins.foldl' (acc: key:

     

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               acc + builtins.getAttr key finalStates

     

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             ) 0 (builtins.attrNames finalStates);

     

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           in totalTimelines;

     

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       +
       

     

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       in {

     

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         inherit part1 part2;

     

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       }

+113

ts/07/index.ts

···

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       const file = await Bun.file("../../shared/07/input.txt").text();

     

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       const board: string[][] = file

     

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       	.trimEnd()

     

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       	.split("\n")

     

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       	.map((line) => line.split(""));

     

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       type Coord = { r: number; c: number };

     

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       // Find S

     

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       const S: Coord | null = (() => {

     

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       	for (let r = 0; r < board.length; r++) {

     

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       		const c = board[r]?.indexOf("S") as number;

     

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       		if (c !== -1) return { r, c };

     

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       	}

     

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       	return null;

     

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       })();

     

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       +
       

     

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       if (!S) throw "No start position found";

     

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       +
       

     

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       const inBounds = (r: number, c: number) =>

     

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       	r >= 0 && r < board.length && c >= 0 && c < board[0].length;

     

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       +
       

     

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       // Part 1: Count unique beam positions and splits

     

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       (() => {

     

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       	type BeamPosition = [number, number];

     

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       	let activeBeams: BeamPosition[] = [[S.r, S.c]];

     

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       	let totalSplits = 0;

     

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       +
       

     

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       	while (activeBeams.length > 0) {

     

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       		const nextActive: BeamPosition[] = [];

     

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       +
       

     

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       		for (const [r, c] of activeBeams) {

     

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       			const nr = r + 1;

     

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       			const nc = c;

     

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       +
       

     

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       			if (!inBounds(nr, nc)) continue;

     

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       +
       

     

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       			const cell = board[nr][nc];

     

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       +
       

     

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       			if (cell === ".") {

     

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       				nextActive.push([nr, nc]);

     

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       			} else if (cell === "^") {

     

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       				totalSplits++;

     

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       				// Split into left and right beams

     

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       				const leftC = nc - 1;

     

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       				const rightC = nc + 1;

     

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       				if (inBounds(nr, leftC)) nextActive.push([nr, leftC]);

     

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       				if (inBounds(nr, rightC)) nextActive.push([nr, rightC]);

     

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       			} else {

     

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       				// 'S' or other chars - continue straight

     

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       				nextActive.push([nr, nc]);

     

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       			}

     

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       		}

     

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       +
       

     

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       		// Remove duplicates

     

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       		const uniqueBeams = [

     

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       			...new Set(nextActive.map(([r, c]) => `${r},${c}`)),

     

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       		].map((s) => s.split(",").map(Number) as BeamPosition);

     

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       +
       

     

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       		activeBeams = uniqueBeams;

     

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       	}

     

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       +
       

     

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       	console.log("part 1:", totalSplits);

     

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       +
       })();

     

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       +
       

     

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       // Part 2: Count total timelines (beams multiply through splitters)

     

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       (() => {

     

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       	let currentStates: Record<string, number> = { [`${S.r},${S.c}`]: 1 };

     

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       +
       

     

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       	for (let step = 0; step < board.length; step++) {

     

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       		const nextStates: Record<string, number> = {};

     

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       +
       

     

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       		for (const [key, count] of Object.entries(currentStates)) {

     

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       			const [r, c] = key.split(",").map(Number);

     

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       			const nr = r + 1;

     

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       +
       

     

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       			if (nr >= board.length) continue;

     

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       			if (!inBounds(nr, c)) continue;

     

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       +
       

     

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       			const cell = board[nr][c];

     

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       +
       

     

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       			if (cell === ".") {

     

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       				const nkey = `${nr},${c}`;

     

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       				nextStates[nkey] = (nextStates[nkey] || 0) + count;

     

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       			} else if (cell === "^") {

     

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       				// Each timeline splits into two

     

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       				const lc = c - 1;

     

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       				const rc = c + 1;

     

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       				if (inBounds(nr, lc)) {

     

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       					const lkey = `${nr},${lc}`;

     

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       					nextStates[lkey] = (nextStates[lkey] || 0) + count;

     

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       				}

     

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       +
       				if (inBounds(nr, rc)) {

     

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       					const rkey = `${nr},${rc}`;

     

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       					nextStates[rkey] = (nextStates[rkey] || 0) + count;

     

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       				}

     

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       			} else {

     

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       				// 'S' or other chars - continue straight

     

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       				const nkey = `${nr},${c}`;

     

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       				nextStates[nkey] = (nextStates[nkey] || 0) + count;

     

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       +
       			}

     

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       +
       		}

     

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       +
       

     

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       +
       		if (Object.keys(nextStates).length === 0) break;

     

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       +
       		currentStates = nextStates;

     

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       +
       	}

     

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       +
       

     

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       +
       	const totalTimelines = Object.values(currentStates).reduce(

     

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       +
       		(a, b) => a + b,

     

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       +
       		0,

     

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       +
       	);

     

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       +
       	console.log("part 2:", totalTimelines);

     

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       +
       })();