Solve 2025-01

2025/01/2025-01.run.xml

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+<component name="ProjectRunConfigurationManager">
+  <configuration default="false" name="2025-01" type="BunRunConfiguration">
+    <option name="program" value="2025/01/run.ts" />
+    <option name="workingDirectory" value="$PROJECT_DIR$" />
+    <method v="2" />
+  </configuration>
+</component>

2025/01/index.test.ts

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+import { describe, expect, it } from 'bun:test';
+import { solveFirst, solveSecond } from './index.ts';
+
+describe('2025-01', () => {
+  const testInput = `L68
+L30
+R48
+L5
+R60
+L55
+L1
+L99
+R14
+L82`;
+  it('first', () => {
+    expect(solveFirst(testInput)).toBe(3);
+  });
+  it('second', () => {
+    expect(solveSecond(testInput)).toBe(6);
+    expect(solveSecond(`R1000`)).toBe(10);
+  });
+});

2025/01/index.ts

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+import { mod } from '../../utils/numbers.ts';
+
+const size = 100;
+const initialValue = 50;
+
+function parseInput(input: string) {
+  const regex = /^([LR])(\d*)$/gm;
+  const match = input.matchAll(regex);
+
+  return Array.from(match, (m) => Number(m[2]) * (m[1] === 'L' ? -1 : 1));
+}
+
+export function solveFirst(input: string): number {
+  let zeros = 0;
+  parseInput(input).reduce((d, r) => {
+    const newDial = (d + r) % size;
+    if (newDial === 0) {
+      zeros++;
+    }
+    return newDial;
+  }, initialValue);
+
+  return zeros;
+}
+export function solveSecond(input: string): number {
+  const rots = parseInput(input);
+
+  let zeros = 0;
+  let dial = initialValue;
+
+  // brute force is easier than thinking
+  for (const rot of rots) {
+    if (rot === 0) {
+      continue;
+    }
+    for (let i = 0; i < Math.abs(rot); i++) {
+      dial = mod(dial + (rot > 0 ? 1 : -1), size);
+      if (dial === 0) {
+        zeros++;
+      }
+    }
+  }
+
+  return zeros;
+}

2025/01/run.ts

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+import { join } from 'path';
+import { solveFirst, solveSecond } from './index.ts';
+
+const input = await Bun.file(join(__dirname, 'input.txt')).text();
+
+const firstAnswer = solveFirst(input);
+
+console.log(firstAnswer);
+
+const secondAnswer = solveSecond(input);
+
+console.log(secondAnswer);