Solve 2024-21

2024/21/2024-21.run.xml

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+<component name="ProjectRunConfigurationManager">
+  <configuration default="false" name="2024-21" type="BunRunConfiguration">
+    <option name="program" value="2024/21/run.ts" />
+    <option name="workingDirectory" value="$PROJECT_DIR$" />
+    <method v="2" />
+  </configuration>
+</component>

2024/21/index.test.ts

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+import { describe, expect, it } from 'bun:test';
+import { solveFirst } from './index.ts';
+
+describe('2024-21', () => {
+  it('first', () => {
+    const testInput = `029A
+980A
+179A
+456A
+379A`;
+    expect(solveFirst(testInput)).toBe(126384);
+  });
+});

2024/21/index.ts

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+import { sumBy } from '../../utils/array.ts';
+import {
+  type Coordinate,
+  type Coordinates,
+  findCoordsOfDigit
+} from '../../utils/coordinates.ts';
+
+const DIRS = [
+  // up
+  [0, -1],
+  // right
+  [1, 0],
+  // down
+  [0, 1],
+  // left
+  [-1, 0]
+] as Coordinates;
+
+const DIRS_LIT = ['^', '>', 'v', '<'];
+const numPad = ['789', '456', '123', '#0A'];
+const dirPad = ['#^A', '<v>'];
+
+const findShortestPaths = (pad: string[], startVal: string, endVal: string) => {
+  const start = findCoordsOfDigit(pad, startVal === '^' ? /\^/g : startVal)[0];
+  const stack: {
+    p: Coordinate;
+    path: string[];
+    cost: number;
+    dirId?: number;
+  }[] = [{ p: start, path: [], cost: 0 }];
+  const seen: Map<string, number> = new Map();
+  const paths: string[][] = [];
+  let minCost = Infinity;
+
+  while (stack.length) {
+    const {
+      cost,
+      dirId,
+      p: [x, y],
+      path
+    } = stack.shift()!;
+    if (dirId !== undefined) {
+      path.push(DIRS_LIT[dirId]);
+    }
+    if (pad[y]?.[x] === endVal) {
+      if (cost < minCost) {
+        paths.length = 0;
+        minCost = cost;
+      }
+      if (cost === minCost) paths.push(path);
+      continue;
+    }
+
+    const k = `${x}_${y}`;
+    if ((seen.get(k) || Infinity) < cost) {
+      continue;
+    }
+    seen.set(k, cost);
+    if (cost > minCost) {
+      continue;
+    }
+
+    DIRS.forEach(([dx, dy], dirId) => {
+      const [px, py] = [x + dx, y + dy];
+      if (pad[py]?.[px] === '#') {
+        return;
+      }
+      stack.push({
+        path: [...path],
+        p: [px, py],
+        dirId,
+        cost: cost + 1
+      });
+    });
+  }
+
+  return paths.map((p) => p.join('') + 'A');
+};
+
+const execute = (
+  pad: string[],
+  code: string,
+  depth: number,
+  memo: Map<string, number> = new Map()
+) => {
+  const k = `${code}_${depth}`;
+  const saved = memo.get(k);
+  if (saved !== undefined) return saved;
+
+  let curPos = 'A';
+  let length = 0;
+
+  for (const nextPos of code.split('')) {
+    const paths = findShortestPaths(pad, curPos, nextPos);
+    if (depth === 0) {
+      length += paths[0].length;
+    } else {
+      length += Math.min(
+        ...paths.map((path) => execute(dirPad, path, depth - 1, memo))
+      );
+    }
+    curPos = nextPos;
+  }
+
+  memo.set(k, length);
+  return length;
+};
+export function solveFirst(input: string): number {
+  return sumBy(
+    input.split('\n'),
+    (code) => parseInt(code) * execute(numPad, code, 2)
+  );
+}
+
+export function solveSecond(input: string): number {
+  return sumBy(
+    input.split('\n'),
+    (code) => parseInt(code) * execute(numPad, code, 25)
+  );
+}

2024/21/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);