Solve 2024-11

2024/11/2024-11.run.xml

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+<component name="ProjectRunConfigurationManager">
+  <configuration default="false" name="2024-11" type="BunRunConfiguration">
+    <option name="program" value="2024/11/run.ts" />
+    <option name="workingDirectory" value="$PROJECT_DIR$" />
+    <method v="2" />
+  </configuration>
+</component>

2024/11/index.test.ts

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+import { describe, expect, it } from 'bun:test';
+import { solve, solveFirstSlow } from './index.ts';
+
+describe('2024-11', () => {
+  const testInput = `125 17`;
+  it('first slow', () => {
+    // it takes too long
+    // so only run while `NODE_ENV=production bun test --coverage`
+    if (process.env.NODE_ENV === 'production') {
+      expect(solveFirstSlow(testInput)).toBe(55312);
+    }
+  });
+  it('first', () => {
+    expect(solve(testInput, 25)).toBe(55312);
+  });
+  it('second', () => {
+    expect(solve(testInput, 75)).toBeGreaterThan(55312);
+  });
+});

2024/11/index.ts

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+import { sumArray } from '../../utils/array.ts';
+import { MultiMap } from '../../utils/multi-map.ts';
+
+export function solveFirstSlow(input: string): number {
+  const stones = input.split(' ');
+
+  for (let i = 0; i < 25; i++) {
+    let j = 0;
+    while (j < stones.length) {
+      const stone = stones[j];
+      if (stone === '0') {
+        stones[j] = '1';
+        j++;
+        continue;
+      }
+      if (stone.length % 2 === 0) {
+        const secondStone = stone.substring(stone.length / 2);
+        stones.splice(j + 1, 0, String(Number(secondStone)));
+        stones[j] = stone.substring(0, stone.length / 2);
+        j += 2;
+        continue;
+      }
+
+      stones[j] = String(Number(stone) * 2024);
+      j++;
+    }
+  }
+
+  return stones.length;
+}
+
+const lookup = new MultiMap<number, [number, string]>();
+
+function splits(stone: string, times: number): number {
+  const lookedUp = lookup.multiGet(times, stone);
+  if (lookedUp !== undefined) {
+    return lookedUp;
+  }
+
+  if (times <= 0) {
+    const result = 1;
+    lookup.multiSet(result, times, stone);
+    return result;
+  }
+  if (stone === '0') {
+    const result = splits('1', times - 1);
+    lookup.multiSet(result, times, stone);
+    return result;
+  }
+  if (stone.length % 2 === 0) {
+    const secondStone = stone.substring(stone.length / 2);
+    const firstStone = stone.substring(0, stone.length / 2);
+    const result =
+      splits(firstStone, times - 1) +
+      splits(String(Number(secondStone)), times - 1);
+
+    lookup.multiSet(result, times, stone);
+    return result;
+  }
+
+  const result = splits(String(Number(stone) * 2024), times - 1);
+
+  lookup.multiSet(result, times, stone);
+  return result;
+}
+
+export function solve(input: string, iterations: number): number {
+  const stones = input.split(' ');
+
+  const count = stones.map((stone) => splits(stone, iterations));
+
+  return sumArray(count);
+}

2024/11/run.ts

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+import { join } from 'path';
+import { solve } from './index.ts';
+
+const input = await Bun.file(join(__dirname, 'input.txt')).text();
+
+const firstAnswer = solve(input, 25);
+
+console.log(firstAnswer);
+
+const secondAnswer = solve(input, 75);
+
+console.log(secondAnswer);