Problem 079

git-svn-id: file:///srv/svn/euler@73 e5f4c3ec-3c0c-11df-b522-21efaa4426b5

e079.py

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+"""By analysing a user's login attempts, can you determine the secret numeric passcode?
+
+A common security method used for online banking is to ask the user for three random characters from a passcode. For example, if the passcode was 531278, they may ask for the 2nd, 3rd, and 5th characters; the expected reply would be: 317.
+
+The text file, keylog.txt, contains fifty successful login attempts.
+
+Given that the three characters are always asked for in order, analyse the file so as to determine the shortest possible secret passcode of unknown length.
+"""
+
+def main():
+  key = []
+  with open('p079/keylog.txt', 'r') as f:
+    while True:
+      line = f.readline()
+      if not line:
+        break
+      prev = None
+      for c in line.strip():
+        c = int(c)
+        if c not in key:
+          if prev:
+            # Place right of prev
+            i = key.index(prev) + 1
+            key.insert(i, c)
+            pass
+          else:
+            key.insert(0, c)
+        elif prev and key.index(c) < key.index(prev):
+          # Move if not right of prev
+          old = key.index(c)
+          key.insert(key.index(prev) + 1, c)
+          key.pop(old)
+          pass
+        prev = c
+  print 'Key:', ''.join(str(c) for c in key)
+
+if __name__ == '__main__':
+  main()

p079/keylog.txt

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+319
+680
+180
+690
+129
+620
+762
+689
+762
+318
+368
+710
+720
+710
+629
+168
+160
+689
+716
+731
+736
+729
+316
+729
+729
+710
+769
+290
+719
+680
+318
+389
+162
+289
+162
+718
+729
+319
+790
+680
+890
+362
+319
+760
+316
+729
+380
+319
+728
+716