Add day 4

javascript/day_04/part2.mjs

@@ -0,0 +1,53 @@
+"use strict";
+
+import { readFile } from "fs/promises";
+
+if (process.argv.length <= 2) {
+	console.error(`Needs more args >:(`).
+	process.exit(0);
+}
+
+const fileToRead = process.argv[2];
+const file = await readFile(fileToRead, `utf-8`);
+
+/** @type {Array<Array<string>>} */
+const wordSearch = [];
+
+for (const line of file.split(`\n`)) {
+	wordSearch.push(line.split(``));
+};
+
+
+let total = 0;
+
+// Iterating the puzzle space, which is reduced by one in both axis'
+// in order to reducing the number of iterations since we can't match
+// along the edges anyway
+for (let y = 1, l1 = wordSearch.length - 1; y < l1; y++) {
+	for (let x = 1, l2 = wordSearch[y].length - 1; x < l2; x++) {
+
+
+		// Short-circuit for performance
+		const middle = wordSearch[y][x];
+		if (`A` !== middle) {
+			continue;
+		};
+
+		try {
+			const ne = wordSearch[y - 1][x + 1];
+			const se = wordSearch[y + 1][x + 1];
+			const sw = wordSearch[y + 1][x - 1];
+			const nw = wordSearch[y - 1][x - 1];
+
+			let valid = ne === nw && se === sw;
+			valid ||= ne === se && nw === sw;
+
+			valid &&= (ne === `M` && se === `S`) || (ne === `S` || se === `M`);
+
+			if (valid) total += 1;
+		} catch (c){console.error(c)}
+
+	};
+};
+
+console.log(`Found ${total} instances of X'd MAS`);