solve day 13

src/2023/day13.js

@@ -0,0 +1,83 @@
+function diff(a, b) {
+  let result = 0;
+  for (let i = 0; i < a.length; i++) {
+    if (a[i] !== b[i]) result++;
+  }
+  return result;
+}
+
+function equals(a, b, state) {
+  if (state.smudges > 0) {
+    const x = diff(a, b);
+    if (x <= state.smudges) {
+      state.smudges -= x;
+      return true;
+    }
+  }
+  return a === b;
+}
+
+function getRowMirror(patch, smudges = 0) {
+  const rows = patch.map(row => row.join(''));
+  for (let i = 0; i < rows.length; i++) {
+    const state = { smudges };
+    let mirror = false;
+    if (i + 1 < rows.length && equals(rows[i], rows[i + 1], state)) {
+      mirror = true;
+      for (let j = 1; i - j >= 0 && i + j + 1 < rows.length; j++) {
+        if (!equals(rows[i - j], rows[i + j + 1], state)) {
+          mirror = false;
+        }
+      }
+    }
+    if (mirror && state.smudges === 0) {
+      return i + 1;
+    }
+  }
+  return 0;
+}
+
+function rotate(patch) {
+  const result = [];
+  for (let i = 0; i < patch[0].length; i++) {
+    const row = patch.map(row => row[i]);
+    result.push(row);
+  }
+  return result;
+}
+
+export function part1(input) {
+  const patches = input
+    .split('\n\n')
+    .map(patch => patch.split('\n').map(row => row.split('')));
+  let result = 0;
+  for (let patch of patches) {
+    const row = getRowMirror(patch);
+    if (row > 0) {
+      result += row * 100;
+      continue;
+    }
+    patch = rotate(patch);
+    const col = getRowMirror(patch);
+    result += row * 100 + col;
+  }
+  return result;
+}
+
+export function part2(input) {
+  const patches = input
+    .split('\n\n')
+    .map(patch => patch.split('\n').map(row => row.split('')));
+  let result = 0;
+  for (let patch of patches) {
+    const row = getRowMirror(patch, 1);
+    if (row > 0) {
+      result += row * 100;
+      continue;
+    }
+    patch = rotate(patch);
+    const col = getRowMirror(patch, 1);
+    result += col;
+  }
+  return result; //?
+}

src/2023/day13.spec.js

@@ -0,0 +1,66 @@
+import { part1, part2 } from './day13.js';
+import readInput from '../utils/read-input.js';
+
+const input = readInput(import.meta.url);
+
+describe('day13 2023', () => {
+  describe('part1', () => {
+    it('should work for part 1 examples', () => {
+      expect(
+        part1(
+          [
+            '#.##..##.',
+            '..#.##.#.',
+            '##......#',
+            '##......#',
+            '..#.##.#.',
+            '..##..##.',
+            '#.#.##.#.',
+            '',
+            '#...##..#',
+            '#....#..#',
+            '..##..###',
+            '#####.##.',
+            '#####.##.',
+            '..##..###',
+            '#....#..#',
+          ].join('\n'),
+        ),
+      ).toEqual(405);
+    });
+
+    it('should work for part 1 input', () => {
+      expect(part1(input)).toEqual(37025);
+    });
+  });
+
+  describe('part2', () => {
+    it('should work for part 2 examples', () => {
+      expect(
+        part2(
+          [
+            '#.##..##.',
+            '..#.##.#.',
+            '##......#',
+            '##......#',
+            '..#.##.#.',
+            '..##..##.',
+            '#.#.##.#.',
+            '',
+            '#...##..#',
+            '#....#..#',
+            '..##..###',
+            '#####.##.',
+            '#####.##.',
+            '..##..###',
+            '#....#..#',
+          ].join('\n'),
+        ),
+      ).toEqual(400);
+    });
+
+    it('should work for part 2 input', () => {
+      expect(part2(input)).toEqual(32854);
+    });
+  });
+});