Solve day 2

Author: paulvanbrenk

.aoc_tiles/tiles/2024/02.png

@@ -1,10 +1,13 @@
 <!-- AOC TILES BEGIN -->
 <h1 align="center">
-  2024 - 2 ⭐ - TypeScript
+  2024 - 4 ⭐ - TypeScript
 </h1>
 <a href="src/2024/day1.ts">
   <img src=".aoc_tiles/tiles/2024/01.png" width="161px">
 </a>
+<a href="src/2024/day2.ts">
+  <img src=".aoc_tiles/tiles/2024/02.png" width="161px">
+</a>
 <h1 align="center">
   2023 - 50 ⭐ - TypeScript
 </h1>

README.md

@@ -5,7 +5,7 @@
   "main": "index.js",
   "scripts": {
     "lint": "prettier -w src/**/*.ts",
-    "run": "tsc -p tsconfig.json && node build/day1.js"
+    "run": "tsc -p tsconfig.json && node build/day2.js"
   },
   "author": "",
   "license": "ISC",

package.json

@@ -0,0 +1,73 @@
+import { input } from './input';
+
+const reps = input.split('\n').map((r) => {
+  return r.split(' ').map((n) => Number.parseInt(n));
+});
+
+// The levels are either all increasing or all decreasing.
+// Any two adjacent levels differ by at least one and at most three.
+
+function part1(reports: number[][]) {
+  let unSafeCount: number = 0;
+
+  for (let r of reports) {
+    const a = r[0];
+    const b = r[1];
+
+    const inc = b > a;
+    for (let i = 1; i < r.length; i++) {
+      const diff = (inc ? -1 : 1) * (r[i - 1] - r[i]);
+      if (diff < 1 || diff > 3) {
+        unSafeCount++;
+        break;
+      }
+    }
+  }
+
+  return reports.length - unSafeCount;
+}
+
+function part2(reports: number[][]) {
+  function check(
+    row: number[],
+    inc: boolean,
+    prev: number,
+    cur: number,
+    hasFix: boolean,
+  ): boolean {
+    if (cur > row.length) {
+      return true;
+    }
+    const diff = (inc ? -1 : 1) * (row[prev] - row[cur]);
+    if (diff < 1 || diff > 3) {
+      if (hasFix) {
+        return false;
+      }
+      return (
+        // skip current or skip previous
+        check(row, inc, prev, cur + 1, true) ||
+        check(row, inc, prev - 1, cur, true)
+      );
+    }
+
+    return check(row, inc, cur, cur + 1, hasFix);
+  }
+
+  let unSafeCount: number = 0;
+
+  for (let r of reports) {
+    if (
+      !check(r, true, 0, 1, false) &&
+      !check(r, false, 0, 1, false) &&
+      !check(r, true, 1, 2, true) &&
+      !check(r, false, 1, 2, true)
+    ) {
+      unSafeCount++;
+    }
+  }
+
+  return reports.length - unSafeCount;
+}
+
+console.log(part1(reps));
+console.log(part2(reps));