Solve problem 112 and add custom cache decorator

python/lib_misc.py

@@ -218,3 +218,15 @@ def is_permutation(n, p):
     for p_n in str(p):
         digit_counts_p[int(p_n)] += 1
     return digit_counts_n == digit_counts_p
+
+
+def cache(f):
+    cache = {}
+    def func_cached(*args):
+        if args in cache:
+            return cache[args]
+        r = f(*args)
+        cache[args] = r
+        return r
+    return func_cached
+