feat: 2024 Day 17 Part 1

Author: mfulton26

2024/day/17/part/1/solve.test.ts

@@ -0,0 +1,14 @@
+import solve from "./solve.ts";
+
+import { assertEquals } from "@std/assert";
+
+Deno.test("example", () => {
+  const input = `\
+Register A: 729
+Register B: 0
+Register C: 0
+
+Program: 0,1,5,4,3,0`;
+
+  assertEquals(solve(input), "4,6,3,5,6,3,5,2,1,0");
+});

2024/day/17/part/1/solve.ts

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+export default function solve(input: string) {
+  const [top, bottom] = input.split("\n\n");
+  const output: number[] = [];
+  let [a, b, c] = top.matchAll(/\d+/g)!.map(([v]) => +v);
+  const program = bottom.split(": ")[1].split(",").map(Number);
+  function combo(operand: number) {
+    if (operand < 4) return operand;
+    switch (operand) {
+      case 0:
+      case 1:
+      case 2:
+        return operand;
+      case 4:
+        return a;
+      case 5:
+        return b;
+      case 6:
+        return c;
+      default:
+        throw new Error(`unsupported combo literal: ${operand}`);
+    }
+  }
+  function div(operand: number) {
+    return Math.trunc(a / 2 ** combo(operand));
+  }
+  for (let ip = 0; ip in program;) {
+    const opcode = program[ip++];
+    const operand = program[ip++];
+    switch (opcode) {
+      case 0: // adv
+        a = div(operand);
+        break;
+      case 1: // bxl
+        b = b ^ operand;
+        break;
+      case 2: // bst
+        b = combo(operand) % 8;
+        break;
+      case 3: // jnz
+        if (a) ip = operand;
+        break;
+      case 4: // bxc
+        b ^= c;
+        break;
+      case 5: // out
+        output.push(combo(operand) % 8);
+        break;
+      case 6: // bdv
+        b = div(operand);
+        break;
+      case 7: // cdv
+        c = div(operand);
+        break;
+    }
+  }
+  return output.join(",");
+}