AoC2025: day 4 part 1

Author: martapanc

2024-2025/src/2025/day04/day04.test.ts

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+import {part1, part2} from "./day04";
+
+describe('2025 Day 4', () => {
+    test('Part 1', async () => {
+        expect(await part1('testInput1')).toEqual(13);
+        expect(await part1('input')).toEqual(1372);
+    });
+
+    test('Part 2', async () => {
+        // expect(await part2('testInput1')).toEqual(31);
+        // expect(await part2('input')).toEqual(29379307);
+    });
+});

2024-2025/src/2025/day04/day04.ts

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+import path from "node:path";
+import {readInputLineByLine} from "@utils/io";
+import {Coord, getNeighbors, Grid, readLinesToGrid} from "@utils/grid";
+
+export async function part1(inputFile: string) {
+    return await day4(inputFile, findAccessiblePaperRolls);
+}
+
+export async function part2(inputFile: string) {
+    return await day4(inputFile);
+}
+
+async function day4(inputFile: string, calcFn?: (grid: Grid) => number) {
+    const inputPath = path.join(__dirname, inputFile);
+    const lines = await readInputLineByLine(inputPath);
+    const { grid } = readLinesToGrid(lines);
+    return calcFn?.(grid);
+}
+
+function findAccessiblePaperRolls(grid: Grid) {
+    let paperRolls = 0;
+
+    grid.forEach((value, coord) => {
+        if (value === '@') {
+            const adjacentCells = getNeighbors(Coord.deserialize(coord), grid, true);
+            const rolls = adjacentCells.filter(cell => cell === '@').length;
+            if (rolls < 4)
+                paperRolls += 1;
+        }
+    });
+
+    return paperRolls;
+}

2024-2025/src/2025/day04/testInput1

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+@.@@@@..@.
+@@.@@@@.@@
+.@@@@@@@.@
+.@.@.@.@@@
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+.@@@@@@@@.
+@.@.@@@.@.