17/2024

Author: breadadams

2024/17/example.txt

@@ -0,0 +1,5 @@
+Register A: 729
+Register B: 0
+Register C: 0
+
+Program: 0,1,5,4,3,0

2024/17/index.test.ts

@@ -0,0 +1,33 @@
+import { expect, describe, test } from "bun:test";
+import { part1, part2 } from ".";
+import { getInputs } from "../../utils/get-inputs";
+
+const { exampleInput, puzzleInput } = await getInputs("2024/17");
+
+describe("part 1", () => {
+  test("example", () => {
+    expect(part1(exampleInput)).toBe("4,6,3,5,6,3,5,2,1,0");
+  });
+
+  test("puzzle", () => {
+    expect(part1(puzzleInput)).toBe("7,1,3,4,1,2,6,7,1");
+  });
+});
+
+const exampleInputForPart2 = `
+Register A: 2024
+Register B: 0
+Register C: 0
+
+Program: 0,3,5,4,3,0
+`.trim();
+
+describe("part 2", () => {
+  test("example", () => {
+    expect(part2(exampleInputForPart2)).toBe("117440");
+  });
+
+  test("puzzle", () => {
+    expect(part2(puzzleInput)).toBe("109019476330651");
+  });
+});

2024/17/index.ts

@@ -0,0 +1,127 @@
+import { timePart1, timePart2 } from "../../utils/time-part";
+
+const parseInput = (input: string) => {
+  const [registers, program] = input.split("\n\n");
+
+  const [a, b, c] = registers
+    .split("\n")
+    .map((register) => BigInt(register.split(": ")[1]));
+
+  return {
+    registers: { a, b, c },
+    program: program.split(": ")[1].split(",").map(BigInt),
+  };
+};
+
+const modulo = (a: bigint, b: bigint) => ((a % b) + b) % b;
+
+const getComboOperand = (
+  literalOperand: bigint,
+  registers: ReturnType<typeof parseInput>["registers"]
+) => {
+  if (literalOperand === 4n) return registers.a;
+  if (literalOperand === 5n) return registers.b;
+  if (literalOperand === 6n) return registers.c;
+
+  return literalOperand;
+};
+
+const runProgram = ({ program, registers }: ReturnType<typeof parseInput>) => {
+  let output: bigint[] = [];
+
+  let i = 0;
+  while (true) {
+    if (i >= program.length) {
+      break;
+    }
+
+    const opcode = program[i];
+    const operandIndex = i + 1;
+
+    if (operandIndex >= program.length) {
+      break;
+    }
+
+    const literalOperand = program[operandIndex];
+    const comboOperand = getComboOperand(literalOperand, registers);
+
+    // adv
+    if (opcode === 0n) {
+      registers.a = registers.a / 2n ** comboOperand;
+    }
+
+    // bxl
+    if (opcode === 1n) {
+      registers.b = registers.b ^ literalOperand;
+    }
+
+    // bst
+    if (opcode === 2n) {
+      registers.b = modulo(comboOperand, 8n);
+    }
+
+    // jnz
+    if (opcode === 3n && registers.a !== 0n) {
+      i = Number(literalOperand);
+      continue;
+    }
+
+    // bxc
+    if (opcode === 4n) {
+      registers.b = registers.b ^ registers.c;
+    }
+
+    // out
+    if (opcode === 5n) {
+      output.push(modulo(comboOperand, 8n));
+    }
+
+    // bdv
+    if (opcode === 6n) {
+      registers.b = registers.a / 2n ** comboOperand;
+    }
+
+    // cdv
+    if (opcode === 7n) {
+      registers.c = registers.a / 2n ** comboOperand;
+    }
+
+    // Skip operand
+    i += 2;
+  }
+
+  return output.join(",");
+};
+
+export const part1 = timePart1((input: string) => {
+  const { program, registers } = parseInput(input);
+
+  return runProgram({ program, registers });
+});
+
+export const part2 = timePart2((input: string) => {
+  const { program, registers } = parseInput(input);
+
+  const programStr = program.join(",");
+  let a = 0n;
+
+  while (true) {
+    const output = runProgram({ program, registers: { ...registers, a } });
+
+    if (output === programStr) {
+      break;
+    }
+
+    // Once we _start_ to find a match
+    if (programStr.indexOf(output) + output.length === programStr.length) {
+      // Just increment in instances of 8 times the value of the `A` register
+      a = a * 8n;
+
+      continue;
+    }
+
+    a++;
+  }
+
+  return a.toString();
+});

README.md

@@ -6,6 +6,7 @@
 
 |                    Day                     | Part 1 | Part 2 |
 | :----------------------------------------: | :----: | :----: |
+| [17](https://adventofcode.com/2024/day/17) |   ✅   |   ✅   |
 | [16](https://adventofcode.com/2024/day/16) |   ✅   |   ✅   |
 | [15](https://adventofcode.com/2024/day/15) |   ✅   |   ✅   |
 | [14](https://adventofcode.com/2024/day/14) |   ✅   |   ✅   |