Day 24

1 year ago · b4aaa46c5c
2 changed files with 184 additions and 0 deletions
--- a/24/input
+++ b/24/input
@ -0,0 +1,22 @@
+#.######################################################################################################################################################
+#>.^v.>^v>><>>^>>v>v^>.<>^.>v^v>..<<><>>>v.><^<.>^.<^>^v^>>v<^>><.^<^.<v>v><><^^<^>>^<<<>.>.>^^^<^<^>.>^v.>.>^>^v<<^^<>><vv<><>>>v^.>^<vvv>.^>v.>.v<v.<#
+#<^^^><<vv<vv^^><>><>vv.vv<>vvvv<vv.>^>^>v^vvv>.<^>v<>>.<><<><>v<v^^<^.v^^><<><^><<.v.vv<<><.<<<<v^^>><^<><^<<<<.>v<^v<v>^>>>><.v>^>.>^<^>>v<v<^vv<v>v<#
+#>>>>^.>.^v>v<.^<^vv^^^<>.>>.>><<.v<v^><^><.<<<><.^v^^v<><v^v><vv<<v<..<<^<.<>^<^v.^>^<v^v.^<v>v<><>>>^v<v.^^<><>><>v<^v>>>^v<v^>v<^vvv><v>^><<><^v>>^>#
+#><<>^>v>.<^^v><v.<>v^<<<>^^v>^.v<<>><>v.v>v^.v>>>^<^><.>>v<<<>vv^.>^>^<><^.>.v^^<v<.^>^><>^<v>vv^v>v^<>><<vv>>>v^^<^v>>>v.<<>.v<><^^v<.^>v>.<^^><vv.^>#
+#<.v^vv^vv>><v>^>>^.vvv^^<v<.v^>><<>v<v<<^<<<vv.>><>v.^>vvv<v<v>^<>>v><.>^.>.^<<<.^vvv>^..^>>.v<v.^v^<^^<<^<^>^v>^v<vvv.v^^v<<<>^v<<<v><>v^<<^><.v>v<v>#
+#<^v^><>v^<.>vv>.^<<<vv^^<><^<^.^^<.^vv^>v^^.^<^>^.^<><><^<<>><vv<v^<>v<><>v^^v<.<v^<v>vvv>^>>^<^><>>^vv<^>><v><^.<<v><v.>^v^v>>>^<vv>v<^<><>.^^>.v><<>#
+#<.><^v>^<.>>v<v>v<^v^v.^>v<.v>.<vv>^>v<v<<>^^.<>.<.vvv<^>v^.^<^v>^.>.v<.v>><<<^vv^.^<<^<^v<v^^^>.><>v.^^.^><<.<vvvv<v><<^vv.<^^^^>^<.<><<>>^>v>.^^v.<<#
+#<<^.>v<><>.^>>^v<<^>vv<^v>><.<v^v^<<><v><^^.^^^>^.><^>v^v<<<<>>^>v>^v<^<>..v<.<v<><>v^>v^^v..<>^<><>^v<<v<<><<.v>...>^^v>.>v^.^>vv>^v<>v><<^.>^^..<<^<#
+#><v^<^..>>v<v.<>vvv>v<v^>>>.v^<^v<>.>^<.<<^<>.<..>.^.>^^>.^.^^>v.v^>v<^>^v.<v^>v^^^vv><^>^>>>v><v<>>>..v.<^<.<<<>>><^<<v>>^<.>^^^<><^<.<^>^<v.^>vv>vv>#
+#<><>v^..>v>^^^^<.v>v>..<>><^><<^v.v.<v^<v><><<<v>>>^^>>v<<>^^<^^^>v.<<>v^<v><v^<<v>>^v>>v><v^^>vv^<^v<^v^.><>vv>>>.>>v^<v^v>><^^v.^<v.><v^^<<<v^>>^v^>#
+#>v><>><<^.>v^.v<<<v><^vv<.v^>v<.>vv>v>>^<^<<><>v>v<v..v<^<.vvv<^>^^v<^.>.^^^>^^v.^.>^>>>^><v<.v<^^^^.v.vv<<vv<.>v<^>v^<<vv^v><v>v^>>v.^.^<<.vv>^^^<^v<#
+#<v^<>>^>>^..vv<^<<<v.v.^vv<.<^^<v^<.>^<.^.<<v^^^<^><>.>>>><^<>^>^v>><v^>v.<.^<v>^^>><><.>^v^>^<>^<^^.<^>^^^^^^vv<>vv^v^v>^v^<v<vv><<vv<^^^.>>^><<<.^>>#
+#<.<v^.>>><vv^.<^^^>>>.><v<v>^<>>.^^vv>>^<<<^v><^^<v<>>^^^^<v^<>^^>><^>v^<<>>v<^.>vvvv>>^<.^>.v<^^<<v>>.vv.v^v<>>>><^v^>>>.v.^^v<<v>v^^>^v>^v<><.v><^v.#
+#><<^v><<<.v<^^><^v<^v.<<<.^^.v>vvvv>^>><^^v<>.<>><<.v^>..^<>.><^>^>^v^^>v<<vv>^>vvv.>^^>^^<<>v>v^>^^^<^v>.v>^<><^<.v<^><<>^.^>>><<v^>v^v^v<^v>>^^^><^<#
+#<^>v<>.>>^.v>^<v><>.v.^^v>^<..v.^>^>.v>>><vv^<>^^>v><>vv.<v<v^vv<.^vv<><v>>>^v><v^vvvvv.<vv>>^v<<.v>v^>v><<<^.<<<<>vv>^>>^<>^^<vvv^<vvvvvv><^^<<<>^^<>#
+#>>.>>.^>..<^<^.<<v<><>..^^<..v<.><^^<v.v^v><>^vv<v<^v<^>.v<vvvv><<<>^>^v^>v<>><vv^v<>>>>>v<v<>^.>><v<v.>><v<v^^<v.<><.<>^^^^v<<^>>.><<.><.v^^..>>>.v>>#
+#>v<v^^<^vvv.>^<>>v^v.vv^>v^vvvvv<>.v^.v<.><>^>>^<<v<^^v>v><^.>>^><>v<vv>v<<^>^>^.<v>vv<<>^^>^<<>v><v>.<<^.<>><<^<<.^<^<<<.^>.<.vv>v^v<^>vvv>^v<<<<v<<<#
+#<^<>v^.^<><>^<>^>v<v.^v..v..vv^.<.^^>^>^><.vv>>.<^..^^^<^<.^^<^^v^<^.<<<<<v<^<<><v>^v.<<>.^>><^>^v>><<v<>^v^<<^>>v<<^.v<<^vv>>v>^.v^^^<><vv^^<<>.v.<><#
+#..vv<v><^vv>.v<v<^v><vvv>.v>^v^>>vv^.^>v.v^^<<>^^<>^<^^>.<^v<v>^>^<v<<v<>v<^^^>v>><><<><.<<><^<v<<>v^^>>v><>^v^.v>^^v<^><><^v<^<vv.vvv><><<>v<<><>v<.>#
+#>>.<^^>><<<^>v<^^>>^<<>><<.<^^^<^^^<^<v<^<<^><<v<v<^^>vv<<^v>.^<^^>><>^^^.>v>v^<^>>v><<^<^^^>v><<>^^v><>v..<.^^>..vv.<v>>>^<<v^<v^^v>>>>.>vv.>>^v>^v<.#
+######################################################################################################################################################.#
--- a/24/solution.mjs
+++ b/24/solution.mjs
@ -0,0 +1,162 @@
+import { readFileSync } from 'node:fs';
+
+const input = readFileSync('input', 'utf-8');
+
+// Direction
+const D = {
+  R: 0,
+  D: 1,
+  L: 2,
+  U: 3
+};
+
+class Blizzard {
+  constructor(width, height, x, y, direction) {
+    this.width = width;
+    this.height = height;
+    this.x = x;
+    this.y = y;
+    this.direction = direction;
+  }
+
+  posAtTime(t) {
+    switch (this.direction) {
+      case D.R: return [(this.x + t) % this.width, this.y];
+      case D.D: return [this.x, (this.y + t) % this.height];
+      case D.L: return [
+        this.width - 1 - (this.width - 1 - this.x + t) % this.width,
+        this.y
+      ];
+      case D.U: return [
+        this.x,
+        this.height - 1 - (this.height - 1 - this.y + t) % this.height,
+      ];
+    }
+  }
+}
+
+const initialState = input
+  .split('\n')
+  .filter(line => !!line.trim() && !/#.*#.*#/.test(line))
+  .map(line => line.replace(/^#(.*)#$/, '$1'));
+
+const height = initialState.length;
+const width = initialState[0].length;
+
+const blizzards = initialState
+  .flatMap((line, y) => line
+    .split('')
+    .flatMap((c, x) => {
+      let direction;
+      switch (c) {
+        case '>': direction = D.R; break;
+        case 'v': direction = D.D; break;
+        case '<': direction = D.L; break;
+        case '^': direction = D.U; break;
+        case '.': return [];
+        default: throw new Error(`Invalid character: ${c}`);
+      }
+      return [new Blizzard(width, height, x, y, direction)];
+    })
+  );
+
+function lcm(a, b) {
+  const larger = Math.max(a, b);
+  const smaller = Math.min(a, b);
+
+  for (let m = 1; ; m++) {
+    const v = larger * m;
+    if (v % smaller === 0) {
+      return v;
+    }
+  }
+}
+
+class Frame {
+  constructor(blizzards, width, height, t) {
+    this.width = width;
+    this.height = height;
+    this.t = t;
+    this.data = new Array(height).fill().map(_ => '.'.repeat(width));
+    for (const blizzard of blizzards) {
+      const [x, y] = blizzard.posAtTime(t);
+      this.data[y] = (
+        this.data[y].slice(0, x) +
+        '#' +
+        this.data[y].slice(x + 1)
+      );
+    }
+  }
+
+  getPos(x, y) {
+    // Start
+    if (x === 0 && y === -1) {
+      return '.';
+    }
+    if (x === width - 1 && y === this.height) {
+      return '.';
+    }
+    return this.data[y]?.[x] ?? '#';
+  }
+
+  movesFromPos(x, y) {
+    return [
+      [x, y],
+      [x + 1, y],
+      [x, y + 1],
+      [x - 1, y],
+      [x, y - 1]
+    ].filter(pos =>
+      this.getPos(...pos) !== '#'
+    );
+  }
+
+  print() {
+    console.log(this.data.join('\n'));
+  }
+}
+
+const nFrames = lcm(width, height);
+const frames = new Array(nFrames)
+  .fill()
+  .map((_, t) => new Frame(blizzards, width, height, t));
+
+function fastestRoute(start, end, timeOffset = 0) {
+  let positions = [start];
+  for (let t = timeOffset + 1; ; t++) {
+    const frame = frames[t % nFrames];
+
+    const newPositions = [];
+
+    for (const [x, y] of positions) {
+      const moves = frame.movesFromPos(x, y);
+      if (moves.find(move => move[0] === end[0] && move[1] === end[1])) {
+        return t;
+      }
+      newPositions.push(...frame.movesFromPos(x, y));
+    }
+
+    // Remove duplicates and assign to positions
+    positions = newPositions.filter((pos1, i, arr) =>
+      arr.findLastIndex(
+        pos2 => pos1[0] === pos2[0] && pos1[1] === pos2[1]
+      ) === i
+    );
+  }
+}
+
+const start = [0, -1];
+const end = [width - 1, height];
+
+const fastestTime = fastestRoute(start, end);
+console.log('The fastest time to navigate the blizzards is:', fastestTime);
+
+const fastestTimeWithSnacks = fastestRoute(
+  start,
+  end,
+  fastestRoute(end, start, fastestTime)
+);
+console.log(
+  'The fastest time with a return trip for snacks is:',
+  fastestTimeWithSnacks
+);