Solution to day 25

dlofstrom-python/day25.in

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+Begin in state A.
+Perform a diagnostic checksum after 12399302 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 right.
+    - Continue with state C.
+
+In state B:
+  If the current value is 0:
+    - Write the value 0.
+    - 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 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 D.
+  If the current value is 1:
+    - Write the value 1.
+    - Move one slot to the right.
+    - 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 0.
+    - Move one slot to the left.
+    - Continue with state D.
+
+In state E:
+  If the current value is 0:
+    - Write the value 1.
+    - Move one slot to the right.
+    - Continue with state F.
+  If the current value is 1:
+    - Write the value 1.
+    - Move one slot to the left.
+    - Continue with state B.
+
+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 right.
+    - Continue with state E.

dlofstrom-python/day25.py

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+import sys
+import re
+
+input = sys.stdin.read()
+state = re.findall(r'(?<=Begin in state )\w+(?=.)',input)[0]
+steps = int(re.findall(r'(?<=Perform a diagnostic checksum after )[0-9]+(?= steps.)',input)[0])
+input = input.split('In ')
+
+#Generate turing machine state lookup
+lookup = {}
+for l in input:
+    s = re.findall(r'(?<=state )\w+(?=:)',l)
+    if s:
+        s = s[0]
+        i = re.findall(r'(?<=current value is )\w+(?=:)',l)
+        w = re.findall(r'(?<=Write the value )\w+(?=.)',l)
+        m = re.findall(r'(?<=Move one slot to the )\w+(?=.)',l)
+        c = re.findall(r'(?<=Continue with state )\w+(?=.)',l)
+        m = [1 if x=='right' else -1 for x in m]
+        lookup[(s,int(i[0]))] = (int(w[0]),m[0],c[0])
+        lookup[(s,int(i[1]))] = (int(w[1]),m[1],c[1])
+
+#Step through
+strip = {}
+slot = 0
+for i in range(steps):
+    #Read strip value
+    value = 0
+    if strip.has_key(slot):
+        value = strip[slot]
+
+    #State action
+    w, m, c = lookup[(state, value)]
+    strip[slot] = w
+    slot += m
+    state = c
+
+#Count number of 1's on strip
+print "Part 1:", strip.values().count(1)
+
+
+
+
+
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+