From bbab540d22d2bbb751a8d88a51db0e2ab6fe4c8b Mon Sep 17 00:00:00 2001
From: Oliver <oliver@noreply.localhost>
Date: Mon, 1 Dec 2025 00:32:27 -0700
Subject: [PATCH] Add day 4

---
 javascript/day_04/part1.mjs | 80 +++++++++++++++++++++++++++++++++++++
 javascript/day_04/part2.mjs | 53 ++++++++++++++++++++++++
 2 files changed, 133 insertions(+)
 create mode 100644 javascript/day_04/part1.mjs
 create mode 100644 javascript/day_04/part2.mjs

diff --git a/javascript/day_04/part1.mjs b/javascript/day_04/part1.mjs
new file mode 100644
index 0000000..fc6fda6
--- /dev/null
+++ b/javascript/day_04/part1.mjs
@@ -0,0 +1,80 @@
+"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 = [];
+const wordToLookFor = "XMAS"
+
+for (const line of file.split(`\n`)) {
+	wordSearch.push(line.split(``));
+};
+
+const locationTransformers = {
+	north: ([y, x], i) => [y - i, x],
+	northeast: ([y, x], i) => [y - i, x + i],
+	east: ([y, x], i) => [y, x + i],
+	southeast: ([y, x], i) => [y + i, x + i],
+	south: ([y, x], i) => [y + i, x],
+	southwest: ([y, x], i) => [y + i, x - i],
+	west: ([y, x], i) => [y, x - i],
+	northwest: ([y, x], i) => [y - i, x - i],
+}
+
+let total = 0;
+
+// Iterating the puzzle space
+for (let y = 0, l1 = wordSearch.length; y < l1; y++) {
+	for (let x = 0, l2 = wordSearch[y].length; x < l2; x++) {
+
+
+		// Short-circuit for performance
+		const middle = wordSearch[y][x];
+		if (wordToLookFor.at(0) !== middle) {
+			continue;
+		};
+
+		const valid = {
+			north: true,
+			northeast: true,
+			east: true,
+			southeast: true,
+			south: true,
+			southwest: true,
+			west: true,
+			northwest: true,
+		};
+
+		// Compare each direction against the letters in the word.
+		for (const i in wordToLookFor) {
+			const required = wordToLookFor.at(i);
+
+			// Convert the coordinates for each direction then compare
+			for (const direction in locationTransformers) {
+				if (!valid[direction]) continue;
+				const [ newY, newX ] = locationTransformers[direction](
+					[y, x],
+					parseInt(i)
+				);
+
+				try {
+					valid[direction] = wordSearch[newY][newX] === required;
+				} catch {
+					valid[direction] = false;
+				};
+			};
+		};
+
+		total += Object.values(valid).filter(v => v).length;
+	};
+};
+
+console.log(`Found ${total} instances of ${wordToLookFor}`);
diff --git a/javascript/day_04/part2.mjs b/javascript/day_04/part2.mjs
new file mode 100644
index 0000000..1ef34be
--- /dev/null
+++ b/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`);