advent-of-code

commit 86c5dfa4409581e348bb8027037abdd7ccba9435
parent 71d2698f9ff0d33b8a65d46825e2e12ad01802e7
Author: finwo <finwo@pm.me>
Date:   Wed, 24 Dec 2025 15:19:02 +0100

Completed 2025/02

Diffstat:
A
2025/02/example.txt
 | 
1
+
A
2025/02/index.js
 | 
80
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

2 files changed, 81 insertions(+), 0 deletions(-)
diff --git a/2025/02/example.txt b/2025/02/example.txt
@@ -0,0 +1 @@
+11-22,95-115,998-1012,1188511880-1188511890,222220-222224,1698522-1698528,446443-446449,38593856-38593862,565653-565659,824824821-824824827,2121212118-2121212124
diff --git a/2025/02/index.js b/2025/02/index.js
@@ -0,0 +1,80 @@
+#!/usr/bin/env node
+
+const fs = require('node:fs');
+
+const ranges = fs
+  .readFileSync('input', 'utf-8')
+  .split('\r\n').join(',')
+  .split('\r').join(',')
+  .split('\n').join(',')
+  .split(',')
+  .map(str => str.trim())
+  .filter(str => str)
+
+const totalPart1 = [];
+const totalPart2 = [];
+
+// Part 1 solution
+for(const range of ranges) {
+  let [start, end] = range.split('-');
+  start = parseInt(start, 10);
+  end   = parseInt(end  , 10);
+  const rangePart1Invalid = [];
+  for(
+    let current = start;
+    current <= end;
+    current++
+  ) {
+    const stringified = current.toString(10);
+    const halves      = [
+      stringified.slice(0, stringified.length / 2),
+      stringified.slice(stringified.length / 2),
+    ];
+    if (halves[0] === halves[1]) {
+      rangePart1Invalid.push(current);
+    }
+  }
+  process.stdout.write(`${range} has ${rangePart1Invalid.length} invalid IDs: ${rangePart1Invalid.join(', ')}\n`);
+  totalPart1.push(...rangePart1Invalid);
+}
+
+const part1 = totalPart1.reduce((r,a) => r+a, 0);
+process.stdout.write('\n\n');
+
+// Part 2 solution
+for(const range of ranges) {
+  let [start, end] = range.split('-');
+  start = parseInt(start, 10);
+  end   = parseInt(end  , 10);
+  const rangePart2Invalid = [];
+  for(
+    let current = start;
+    current <= end;
+    current++
+  ) {
+    const stringified = current.toString(10);
+
+    for(let sublength = 1 ; sublength <= (stringified.length / 2) ; sublength++) {
+
+      // Not integer-divisible = not composite of substring
+      if (stringified.length % sublength) continue;
+      let repetitions = stringified.length / sublength;
+
+      if (stringified.slice(0, sublength).repeat(repetitions) === stringified) {
+        rangePart2Invalid.push(current);
+        break;
+      }
+
+    }
+
+  }
+  process.stdout.write(`${range} has ${rangePart2Invalid.length} invalid IDs: ${rangePart2Invalid.join(', ')}\n`);
+  totalPart2.push(...rangePart2Invalid);
+}
+
+const part2 = totalPart2.reduce((r,a) => r+a, 0);
+process.stdout.write('\n\n');
+
+
+process.stdout.write(`------[ Part 1: ${part1} ]------\n`);
+process.stdout.write(`------[ Part 2: ${part2} ]------\n\n`);