feat(js): add solutions for 2023 day 10

js/src/2023/10/index.js

@@ -0,0 +1,119 @@
+/* eslint-disable consistent-return, quote-props */
+
+import { Grid, Orientation, dx, dy, solution } from '../../utils';
+
+const PIPES = {
+  '|': { // vertical pipe connecting north and south.
+    [Orientation.UP]: Orientation.UP,
+    [Orientation.DOWN]: Orientation.DOWN,
+  },
+  '-': { // horizontal pipe connecting east and west.
+    [Orientation.LEFT]: Orientation.LEFT,
+    [Orientation.RIGHT]: Orientation.RIGHT,
+  },
+  'L': { // 90-degree bend connecting north and east.
+    [Orientation.DOWN]: Orientation.RIGHT,
+    [Orientation.LEFT]: Orientation.UP,
+  },
+  'J': { // 90-degree bend connecting north and west.
+    [Orientation.DOWN]: Orientation.LEFT,
+    [Orientation.RIGHT]: Orientation.UP,
+  },
+  '7': { // 90-degree bend connecting south and west.
+    [Orientation.UP]: Orientation.LEFT,
+    [Orientation.RIGHT]: Orientation.DOWN,
+  },
+  'F': { // 90-degree bend connecting south and east.
+    [Orientation.UP]: Orientation.RIGHT,
+    [Orientation.LEFT]: Orientation.DOWN,
+  },
+};
+
+const parse = (input) => Grid.from(input.trim());
+
+const traverse = (grid, start) => {
+  // Does not matter which orientation to start with (as it is a loop)
+  let orientation = Object.values(PIPES[start.value])[0];
+
+  let current = start;
+  const path = [];
+  do {
+    const next = grid.getPoint(current.x + dx(orientation), current.y + dy(orientation));
+    const directions = PIPES[next?.value];
+    if (!directions || !(orientation in directions)) {
+      return null;
+    }
+    orientation = directions[orientation];
+    path.push(next);
+    current = next;
+  } while (current !== start);
+  return path;
+};
+
+const findLoop = (grid) => {
+  const start = grid.find((point) => point.value === 'S');
+
+  // What's that? Brute-force again? Yes.
+  for (const variant of Object.keys(PIPES)) {
+    start.value = variant;
+    const path = traverse(grid, start);
+    if (path) {
+      return path;
+    }
+  }
+};
+
+export const partOne = solution((input) => {
+  const grid = parse(input);
+  const loop = findLoop(grid);
+  return loop.length / 2;
+});
+
+export const partTwo = solution((input) => {
+  const grid = parse(input);
+  const loop = findLoop(grid);
+
+  let area = 0;
+
+  // See: https://en.wikipedia.org/wiki/Point_in_polygon#Ray_casting_algorithm
+  let y = 0;
+  let enclosed = false;
+  let edge = null;
+  for (const point of grid) {
+    if (point.y > y) {
+      enclosed = false;
+      edge = null;
+      y = point.y;
+    }
+
+    const onLoop = loop.includes(point);
+
+    const { value } = point;
+    if (onLoop && value !== '-') {
+      // Sweet jesus, this took way too long to figure out :')
+
+      // When dealing with a boxed edge: ┌─┐ or └─┘
+      if ((edge === 'F' && value === '7') || (edge === 'L' && value === 'J')) {
+        enclosed = !enclosed;
+        edge = null;
+
+      // When dealing with a bend: ┌─┘ or └─┐
+      } else if ((edge === 'F' && value === 'J') || (edge === 'L' && value === '7')) {
+        edge = null;
+
+      // Mark as intersection for all other cases and handle edge entry: ┌─ or └─
+      } else {
+        enclosed = !enclosed;
+        if (value === 'F' || value === 'L') {
+          edge = value;
+        }
+      }
+    }
+
+    if (!onLoop && enclosed) {
+      ++area;
+    }
+  }
+
+  return area;
+});

puzzles/2023/10/examples.yaml

@@ -0,0 +1,67 @@
+part-one:
+  - input: |
+      .....
+      .S-7.
+      .|.|.
+      .L-J.
+      .....
+    answer: 4
+
+  - input: |
+      ..F7.
+      .FJ|.
+      SJ.L7
+      |F--J
+      LJ...
+    answer: 8
+
+part-two:
+  - input: |
+      ...........
+      .S-------7.
+      .|F-----7|.
+      .||.....||.
+      .||.....||.
+      .|L-7.F-J|.
+      .|..|.|..|.
+      .L--J.L--J.
+      ...........
+    answer: 4
+
+  - input: |
+      ..........
+      .S------7.
+      .|F----7|.
+      .||OOOO||.
+      .||OOOO||.
+      .|L-7F-J|.
+      .|II||II|.
+      .L--JL--J.
+      ..........
+    answer: 4
+
+  - input: |
+      .F----7F7F7F7F-7....
+      .|F--7||||||||FJ....
+      .||.FJ||||||||L7....
+      FJL7L7LJLJ||LJ.L-7..
+      L--J.L7...LJS7F-7L7.
+      ....F-J..F7FJ|L7L7L7
+      ....L7.F7||L7|.L7L7|
+      .....|FJLJ|FJ|F7|.LJ
+      ....FJL-7.||.||||...
+      ....L---J.LJ.LJLJ...
+    answer: 8
+
+  - input: |
+      FF7FSF7F7F7F7F7F---7
+      L|LJ||||||||||||F--J
+      FL-7LJLJ||||||LJL-77
+      F--JF--7||LJLJ7F7FJ-
+      L---JF-JLJ.||-FJLJJ7
+      |F|F-JF---7F7-L7L|7|
+      |FFJF7L7F-JF7|JL---7
+      7-L-JL7||F7|L7F-7F7|
+      L.L7LFJ|||||FJL7||LJ
+      L7JLJL-JLJLJL--JLJ.L
+    answer: 10