2025: day4: ts

AdventOfCode2025/day4/.gitignore

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+# dependencies (bun install)
+node_modules
+
+# output
+out
+dist
+*.tgz
+
+# code coverage
+coverage
+*.lcov
+
+# logs
+logs
+_.log
+report.[0-9]_.[0-9]_.[0-9]_.[0-9]_.json
+
+# dotenv environment variable files
+.env
+.env.development.local
+.env.test.local
+.env.production.local
+.env.local
+
+# caches
+.eslintcache
+.cache
+*.tsbuildinfo
+
+# IntelliJ based IDEs
+.idea
+
+# Finder (MacOS) folder config
+.DS_Store

AdventOfCode2025/day4/README.md

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+# day4
+
+To install dependencies:
+
+```bash
+bun install
+```
+
+To run:
+
+```bash
+bun run index.ts
+```
+
+This project was created using `bun init` in bun v1.2.8. [Bun](https://bun.sh) is a fast all-in-one JavaScript runtime.

AdventOfCode2025/day4/bun.lock

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+{
+  "lockfileVersion": 1,
+  "workspaces": {
+    "": {
+      "name": "day4",
+      "devDependencies": {
+        "@types/bun": "latest",
+      },
+      "peerDependencies": {
+        "typescript": "^5",
+      },
+    },
+  },
+  "packages": {
+    "@types/bun": ["@types/bun@1.3.3", "", { "dependencies": { "bun-types": "1.3.3" } }, "sha512-ogrKbJ2X5N0kWLLFKeytG0eHDleBYtngtlbu9cyBKFtNL3cnpDZkNdQj8flVf6WTZUX5ulI9AY1oa7ljhSrp+g=="],
+
+    "@types/node": ["@types/node@24.10.1", "", { "dependencies": { "undici-types": "~7.16.0" } }, "sha512-GNWcUTRBgIRJD5zj+Tq0fKOJ5XZajIiBroOF0yvj2bSU1WvNdYS/dn9UxwsujGW4JX06dnHyjV2y9rRaybH0iQ=="],
+
+    "bun-types": ["bun-types@1.3.3", "", { "dependencies": { "@types/node": "*" } }, "sha512-z3Xwlg7j2l9JY27x5Qn3Wlyos8YAp0kKRlrePAOjgjMGS5IG6E7Jnlx736vH9UVI4wUICwwhC9anYL++XeOgTQ=="],
+
+    "typescript": ["typescript@5.9.3", "", { "bin": { "tsc": "bin/tsc", "tsserver": "bin/tsserver" } }, "sha512-jl1vZzPDinLr9eUt3J/t7V6FgNEw9QjvBPdysz9KfQDD41fQrC2Y4vKQdiaUpFT4bXlb1RHhLpp8wtm6M5TgSw=="],
+
+    "undici-types": ["undici-types@7.16.0", "", {}, "sha512-Zz+aZWSj8LE6zoxD+xrjh4VfkIG8Ya6LvYkZqtUQGJPZjYl53ypCaUwWqo7eI0x66KBGeRo+mlBEkMSeSZ38Nw=="],
+  }
+}

AdventOfCode2025/day4/index.ts

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+const file = Bun.file("./input.txt");
+const content = await file.text();
+
+const EMPTY = ".";
+const PAPER = "@";
+
+const splitContent = [...content.trim().split("\n")]
+const lineSize = splitContent[0]!.length
+
+const grid = [
+    '.'.repeat(lineSize),
+    ...splitContent,
+    '.'.repeat(lineSize),
+].map(l => `.${l}.`.split(""))
+
+const solve = (grid: string[][]): [number, string[][]] => {
+    let paperRemoved = 0;
+    const newGrid = structuredClone(grid)
+
+    for (let y = 1; y < grid.length - 1; y++) {
+        for (let x = 1; x < grid[0]!.length - 1; x++) {
+            let adjacentPapers = 0;
+
+            const currentSquare = grid?.[y]?.[x]
+            if (!currentSquare) {
+                throw new Error("current square must be defined")
+            }
+
+            if (currentSquare === EMPTY) {
+                continue
+            }
+
+            for (let yOffset = -1; yOffset <= 1; yOffset++) {
+                for (let xOffset = -1; xOffset <= 1; xOffset++) {
+                    if (yOffset === 0 && xOffset === 0) {
+                        continue
+                    }
+
+                    const square = grid![y + yOffset]![x + xOffset]!
+                    if (square === PAPER) {
+                        adjacentPapers++
+                    }
+                }
+            }
+
+            if (adjacentPapers < 4) {
+                newGrid![y]![x] = EMPTY
+                paperRemoved++
+            }
+        }
+    }
+
+    return [paperRemoved, newGrid]
+}
+
+const removePaper = (grid: string[][]): number => {
+    let totalPaperRemoved = 0;
+    let currentGrid = grid
+
+    while (true) {
+        const [paperRemoved, newGrid] = solve(currentGrid)
+        currentGrid = newGrid
+
+        if (paperRemoved === 0) {
+            break
+        }
+
+        totalPaperRemoved += paperRemoved
+    }
+
+    return totalPaperRemoved
+}
+
+const [part1] = solve(grid)
+const part2 = removePaper(grid)
+
+console.log("Part 1: ", part1)
+console.log("Part 2: ", part2)

AdventOfCode2025/day4/package.json

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+{
+  "name": "day4",
+  "module": "index.ts",
+  "type": "module",
+  "private": true,
+  "devDependencies": {
+    "@types/bun": "latest"
+  },
+  "peerDependencies": {
+    "typescript": "^5"
+  }
+}

AdventOfCode2025/day4/tsconfig.json

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+{
+  "compilerOptions": {
+    // Environment setup & latest features
+    "lib": ["ESNext"],
+    "target": "ESNext",
+    "module": "ESNext",
+    "moduleDetection": "force",
+    "jsx": "react-jsx",
+    "allowJs": true,
+
+    // Bundler mode
+    "moduleResolution": "bundler",
+    "allowImportingTsExtensions": true,
+    "verbatimModuleSyntax": true,
+    "noEmit": true,
+
+    // Best practices
+    "strict": true,
+    "skipLibCheck": true,
+    "noFallthroughCasesInSwitch": true,
+    "noUncheckedIndexedAccess": true,
+
+    // Some stricter flags (disabled by default)
+    "noUnusedLocals": false,
+    "noUnusedParameters": false,
+    "noPropertyAccessFromIndexSignature": false
+  }
+}