Day 8

08/part2.js

@@ -0,0 +1,61 @@
+const fs = require('fs');
+
+function parseLine(line) {
+  let [ op, offset ] = line.split(' ');
+
+  return { op: op, offset: Number(offset), visited: false };
+}
+
+function run(program) {
+  let acc = 0;
+  let pc = 0;
+
+  while(true) {
+    if (pc == program.length) {
+      return acc;
+    };
+
+    let insn = program[pc];
+    if (insn.visited) {
+      return undefined;
+    };
+
+    insn.visited = true;
+
+    switch (insn.op) {
+    case 'nop':
+      pc++;
+      break;
+    case 'jmp':
+      pc = pc + insn.offset;
+      break;
+    case 'acc':
+      acc = acc + insn.offset;
+      pc++;
+      break;
+    }
+  }
+}
+
+fs.readFile('input', (err, data) => {
+  if (err) throw err;
+  let program = data.toString().trim().split("\n").map( parseLine ).flat();
+
+  for(i=0; i<program.length; i++) {
+    let copy = JSON.parse(JSON.stringify(program))
+    let insn = copy[i];
+
+   if (insn.op == 'nop') {
+      insn.op = 'jmp';
+    } else if (insn.op == 'jmp') {
+      insn.op = 'nop';
+    } else {
+      continue; // If we don't make any changes, the program can't terminate
+    }
+
+    if (result = run(copy)) {
+      console.log(result);
+      return;
+    }
+  }
+});