2020 day 8

2020/08/part2.js

@@ -0,0 +1,48 @@
+const fs = require('fs');
+
+const data = fs.readFileSync('input.txt', 'utf-8');
+const lines = data.split('\n');
+let instructions = [];
+
+lines.forEach((line, i) => {
+  t = line.split(' ');
+  instructions[i] = [t[0], parseInt(t[1])]
+})
+
+function loop (i, seen, acc, swapped) {
+  console.log(i, instructions[i])
+  if (seen.has(i)) {
+    console.log('seen, escaping')
+    return false;
+  }
+  seen.add(i);
+  console.log('acc = ', acc)
+  let nextI = i;
+  let nextAcc = acc;
+  switch (instructions[i][0]) {
+    case 'acc':
+      nextAcc+=instructions[i][1];
+      nextI++;
+      break;
+    case 'jmp':
+      nextI += instructions[i][1];
+      break;
+    case 'nop':
+      nextI ++;
+      break;
+    default:
+      console.log('halting with', acc);
+      return true;
+  }
+  nextAcc = loop(nextI, seen, nextAcc, swapped);
+  if (nextAcc === false) {
+    console.log(i, instructions[i])
+    if (instructions[i][0] == 'jmp' && !swapped) {
+      nextAcc = loop(i+1, seen, acc, true)
+    }
+  }
+  return nextAcc;
+}
+
+loop(0, new Set(), 0, false)
+// take the last acc value