Added day25 solution. Added python-related entries to .gitignore

.gitignore

@@ -3,3 +3,5 @@ debug
 *.exe
 *.o
 *.dll
+__pycache__
+*.pyc

2017/day25/day25.py

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+"""Advent of Code
+day25.py
+Code by Dylan Sheehy
+http://adventofcode.com/2017/day/25
+"""
+
+from turing import Turing
+
+STATES = {
+    'A': [
+        {'write': 1, 'move': 1, 'next': 'B'}, # current value is 0
+        {'write': 0, 'move': -1, 'next': 'C'} # current value is 1
+    ],
+    'B': [
+        {'write': 1, 'move': -1, 'next': 'A'}, # current value is 0
+        {'write': 1, 'move': 1, 'next': 'D'} # current value is 1
+    ],
+    'C': [
+        {'write': 1, 'move': 1, 'next': 'A'}, # current value is 0
+        {'write': 0, 'move': -1, 'next': 'E'} # current value is 1
+    ],
+    'D': [
+        {'write': 1, 'move': 1, 'next': 'A'}, # current value is 0
+        {'write': 0, 'move': 1, 'next': 'B'} # current value is 1
+    ],
+    'E': [
+        {'write': 1, 'move': -1, 'next': 'F'}, # current value is 0
+        {'write': 1, 'move': -1, 'next': 'C'} # current value is 1
+    ],
+    'F': [
+        {'write': 1, 'move': 1, 'next': 'D'}, # current value is 0
+        {'write': 1, 'move': 1, 'next': 'A'} # current value is 1
+    ]
+}
+
+TM = Turing('A', STATES)
+STEPS = 12919244
+for i in range(STEPS):
+    if i % 1000000 == 0:
+        print(i)
+    TM.run()
+
+print(TM.checksum())

2017/day25/input.txt

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+Begin in state A.
+Perform a diagnostic checksum after 12919244 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 C.
+
+In state B:
+  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 1.
+    - Move one slot to the right.
+    - Continue with state D.
+
+In state C:
+  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 0.
+    - Move one slot to the left.
+    - Continue with state E.
+
+In state D:
+  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 0.
+    - Move one slot to the right.
+    - Continue with state B.
+
+In state E:
+  If the current value is 0:
+    - Write the value 1.
+    - Move one slot to the left.
+    - Continue with state F.
+  If the current value is 1:
+    - Write the value 1.
+    - Move one slot to the left.
+    - Continue with state C.
+
+In state F:
+  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 1.
+    - Move one slot to the right.
+    - Continue with state A.

2017/day25/turing.py

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+"""Contains a Turing machine class, and not much else."""
+
+class Turing:
+    "Represents a Turing machine."
+    def __init__(self, start, states):
+        """Creates a Turing machine.
+
+        Creates a Turing machine with the given starting state and state transitions.
+        States should look like this:
+        {
+            'State1': [
+                {'write': value_to_write, 'move': <1 or -1>, 'next': next_state},
+                {'write': value_to_write, 'move': <1 or -1>, 'next': next_state}
+            ],
+            'State2': [...],
+            ...
+        }
+
+        Arguments:
+            start {str} -- The Turing Machine's starting state.
+            steps {int} -- Number of steps to run
+            states {dict} -- State transitions
+
+        """
+        self.current = start
+        self.states = states
+        self.cursor = 0
+        self.tape = {}
+
+    def run(self):
+        """Runs the Turing Maching for one step."""
+        value = self.tape.get(self.cursor, 0)
+        state = self.states[self.current][value]
+        self.tape[self.cursor] = state['write'] # write to the tape
+        self.cursor += state['move']            # move the cursor
+        self.current = state['next']            # go to next state
+
+    def checksum(self):
+        "Returns the number of ones on the tape."
+        return sum(self.tape.values())