2024 day 17

Author: FriendlyUser1

2024/day17/lilcomputer.js

@@ -0,0 +1,58 @@
+const compute = (/** @type {bigint} */ regA) => {
+	let out = [],
+		a = regA,
+		b,
+		c;
+
+	while (a != 0n) {
+		b = a & 7n;
+		b ^= 6n; // Flips 4,2 bits
+		c = a >> b;
+		b ^= c;
+		b ^= 7n; // Flips the bits
+		a >>= 3n;
+		out.push(b & 7n); // Output first 3 bits of b
+	}
+
+	return out;
+};
+
+const input = (await Bun.file("./input.txt").text()).split("\n");
+
+const program = input[4].split(" ")[1].split(","),
+	registerA = BigInt(input[0].split(" ")[2]);
+
+const search = () => {
+	let stack = [];
+
+	stack.push([]);
+
+	while (stack.length > 0) {
+		const ans = stack.pop(),
+			ansLen = ans.length;
+
+		const checkPart = (a) => a.slice(15 - ansLen).join(",");
+
+		// Goal reached
+		if (ansLen == 16) return parseInt(ans.join(""), 8);
+
+		// Our found so far + whatever padding to 16
+		const paddedInput = ans.concat(new Array(16 - ansLen).fill(1));
+
+		for (let i = 0; i < 8; i++) {
+			const testResult = compute(
+				BigInt(parseInt(paddedInput.with(ansLen, i).join(""), 8))
+			);
+
+			// If the end matches the target
+			if (
+				testResult.length == 16 &&
+				checkPart(testResult) == checkPart(program)
+			)
+				stack.push(ans.concat(i));
+		}
+	}
+};
+
+console.log("With given values:", compute(registerA).join(","));
+console.log("Register A to get program output:", search());