Add day 8 part 2

Author: lundgren2

src/2020/day8/part2.ts

@@ -0,0 +1,38 @@
+const runProgram = (program: string[]): number | null => {
+  let accumulator = 0;
+  let stackPointer = 0;
+
+  while (stackPointer < program.length) {
+    const instruction = program[stackPointer];
+    if (instruction === 'EXECUTED') return null; // Loop detected
+
+    const [op, arg] = instruction.split(' ');
+    program[stackPointer] = 'EXECUTED';
+
+    if (op === 'acc') {
+      accumulator += parseInt(arg);
+      stackPointer++;
+    } else if (op === 'jmp') {
+      stackPointer += parseInt(arg);
+    } else if (op === 'nop') {
+      stackPointer++;
+    }
+  }
+
+  return accumulator; // program terminated;
+};
+
+export const part2 = (input: string) => {
+  const instructions = input.split('\n');
+
+  for (let i = 0; i < instructions.length - 1; i++) {
+    const [op, arg] = instructions[i].split(' ');
+    if (op !== 'acc') {
+      // Swap jmp and nop and run new program
+      const newProgram = [...instructions];
+      newProgram[i] = op === 'jmp' ? `nop ${arg}` : `jmp ${arg}`;
+      const result = runProgram(newProgram);
+      if (result) return result;
+    }
+  }
+};

src/2020/day8/test.spec.ts

@@ -1,16 +1,11 @@
 import {readInput} from '../../utils';
 
 import {part1} from './part1';
+import {part2} from './part2';
 
 describe('Advent of Code 2020 - Day 8', () => {
   let input: string;
-  beforeAll(async () => {
-    input = await readInput(__dirname + '/input');
-  });
-
-  describe('part 1', () => {
-    it('should output 5 of test input ', () => {
-      const input = `nop +0
+  const testInput = `nop +0
 acc +1
 jmp +4
 acc +3
@@ -19,11 +14,28 @@ acc -99
 acc +1
 jmp -4
 acc +6`;
-      expect(part1(input)).toBe(5);
+
+  beforeAll(async () => {
+    input = await readInput(__dirname + '/input');
+  });
+
+  describe('part 1', () => {
+    it('should output 5 of test input ', () => {
+      expect(part1(testInput)).toBe(5);
     });
 
     it('should output 1548 from input', () => {
       expect(part1(input)).toBe(1548);
     });
   });
+  describe('part 2', () => {
+    it('should output 8 of test input ', () => {
+      expect(part2(testInput)).toBe(8);
+    });
+
+    it('should output 1375 from input', () => {
+      const output = part2(input);
+      expect(part2(input)).toBe(1375);
+    });
+  });
 });