Added memoize to lib

lib.py

@@ -1,5 +1,15 @@
 #!/usr/bin/env python3
 
+def memoize(f):
+    cache = dict()
+    def memf(*args):
+        key = tuple(args)
+        if key not in cache:
+            cache[key] = f(*args)
+        return cache[key]
+    return memf
+
+
 class Graph(dict):
     nodes = dict.keys