Day 25

25.py

@@ -0,0 +1,63 @@
+import re
+from collections import defaultdict
+
+VALUE = 0
+MOVE = 1
+STATE = 2
+
+
+def parse():
+    begin_state = re.compile(r'Begin in state (.*?)\.')
+    checksum_steps = re.compile(r'Perform a diagnostic checksum after ([0-9]+) steps\.')
+    state_header = re.compile(r'In state (.*?):')
+    value_header = re.compile(r'If the current value is ([01]):')
+    value_action = re.compile(r'- Write the value ([01])\.')
+    move_action = re.compile(r'- Move one slot to the (right|left)\.')
+    state_action = re.compile(r'- Continue with state (.*?)\.')
+
+    initial_state = checksum = None
+    transitions = defaultdict(lambda: [[None]*3, [None]*3])
+    cur_state = None
+    cur_value = None
+
+    with open('data/25.txt') as file:
+        for line in file.readlines():
+            line = line.strip()
+            if len(line) == 0:
+                continue
+
+            if initial_state is None:
+                initial_state = begin_state.match(line).group(1)
+            elif checksum is None:
+                checksum = int(checksum_steps.match(line).group(1))
+            elif cur_state is None:
+                cur_state = state_header.match(line).group(1)
+            elif cur_value is None:
+                cur_value = int(value_header.match(line).group(1))
+            elif transitions[cur_state][cur_value][VALUE] is None:
+                transitions[cur_state][cur_value][VALUE] = int(value_action.match(line).group(1))
+            elif transitions[cur_state][cur_value][MOVE] is None:
+                transitions[cur_state][cur_value][MOVE] = move_action.match(line).group(1)
+            elif transitions[cur_state][cur_value][STATE] is None:
+                transitions[cur_state][cur_value][STATE] = state_action.match(line).group(1)
+                if cur_value == 1:
+                    cur_state = None
+                cur_value = None
+
+    return initial_state, checksum, dict(transitions)
+
+
+def execute(state, rounds, transitions):
+    tape = defaultdict(lambda: 0)
+    head = 0
+    for _ in range(rounds):
+        instr = transitions[state][tape[head]]
+        tape[head] = instr[VALUE]
+        head += 1 if instr[MOVE] == 'right' else -1
+        state = instr[STATE]
+
+    return sum(v for v in tape.values() if v == 1)
+
+
+state, target, transitions = parse()
+print(execute(state, target, transitions))

data/25.txt

@@ -0,0 +1,62 @@
+Begin in state A.
+Perform a diagnostic checksum after 12586542 steps.
+
+In state A:
+  If the current value is 0:
+    - Write the value 1.
+    - Move one slot to the right.
+    - Continue with state B.
+  If the current value is 1:
+    - Write the value 0.
+    - Move one slot to the left.
+    - Continue with state B.
+
+In state B:
+  If the current value is 0:
+    - Write the value 0.
+    - Move one slot to the right.
+    - Continue with state C.
+  If the current value is 1:
+    - Write the value 1.
+    - Move one slot to the left.
+    - Continue with state B.
+
+In state C:
+  If the current value is 0:
+    - Write the value 1.
+    - Move one slot to the right.
+    - Continue with state D.
+  If the current value is 1:
+    - Write the value 0.
+    - Move one slot to the left.
+    - Continue with state A.
+
+In state D:
+  If the current value is 0:
+    - Write the value 1.
+    - Move one slot to the left.
+    - Continue with state E.
+  If the current value is 1:
+    - Write the value 1.
+    - Move one slot to the left.
+    - Continue with state F.
+
+In state E:
+  If the current value is 0:
+    - Write the value 1.
+    - Move one slot to the left.
+    - Continue with state A.
+  If the current value is 1:
+    - Write the value 0.
+    - Move one slot to the left.
+    - Continue with state D.
+
+In state F:
+  If the current value is 0:
+    - Write the value 1.
+    - Move one slot to the right.
+    - Continue with state A.
+  If the current value is 1:
+    - Write the value 1.
+    - Move one slot to the left.
+    - Continue with state E.