From 1ebb5f738eb7045786ca459435e4007f4f1ea011 Mon Sep 17 00:00:00 2001
From: dece <shgck@pistache.land>
Date: Tue, 8 Dec 2020 18:35:35 +0100
Subject: [PATCH] Day 8

---
 2020/day8.py | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)
 create mode 100644 2020/day8.py

diff --git a/2020/day8.py b/2020/day8.py
new file mode 100644
index 0000000..057b441
--- /dev/null
+++ b/2020/day8.py
@@ -0,0 +1,65 @@
+def main():
+    with open("day8.txt", "rt") as f:
+        lines = [line.rstrip() for line in f.readlines()]
+
+    # Part 1
+    visited = set()
+    vm = Vm(lines)
+    while vm.ip not in visited:
+        visited.add(vm.ip)
+        vm.step()
+    print("Acc after revisiting op:", vm.acc)
+
+    # Part 2
+    jmps = reversed([i for i, inst in enumerate(vm.code) if inst[0] == "jmp"])
+    for i in jmps:
+        vm.reset()
+        orig_jmp = vm.code[i]
+        vm.code[i] = ["nop", orig_jmp[1]]
+        if not vm.does_loop():
+            print(vm.acc)
+            return
+    # No need to try for nops apparently!
+
+        
+class Vm:
+
+    def __init__(self, code):
+        self.text = code
+        self.reset()
+
+    def reset(self):
+        self.code = self.parse_code(self.text)
+        self.ip = 0
+        self.acc = 0
+
+    def step(self):
+        inst = self.code[self.ip]
+        if inst[0] == "nop":
+            pass
+        elif inst[0] == "jmp":
+            self.ip += int(inst[1])
+            return
+        elif inst[0] == "acc":
+            self.acc += int(inst[1])
+        self.ip += 1
+
+    def does_loop(self):
+        visited = set()
+        while self.ip < len(self.code):
+            visited.add(self.ip)
+            self.step()
+            if self.ip in visited:
+                return True
+        return False
+
+    @staticmethod
+    def parse_code(code):
+        ops = []
+        for line in code:
+            ops.append(line.split())
+        return ops
+
+
+if __name__ == "__main__":
+    main()