Solve problem 112 and add custom cache decorator

python/e112.py

@@ -0,0 +1,37 @@
+
+def is_increasing(n_str):
+    if len(n_str) < 2:
+        return True
+    if n_str[0] <= n_str[1]:
+        return is_increasing(n_str[1:])
+    return False
+
+
+def is_decreasing(n_str):
+    if len(n_str) < 2:
+        return True
+    if n_str[0] >= n_str[1]:
+        return is_decreasing(n_str[1:])
+    return False
+
+
+def is_bouncy(n_str):
+    return not (is_increasing(n_str) or is_decreasing(n_str))
+
+
+def euler_112():
+    n, n_bouncy = 0, 0
+    while True:
+        n += 1
+        if is_bouncy(str(n)):
+            n_bouncy += 1
+            ratio = n_bouncy / n
+            if ratio >= 0.99:
+                return n
+
+
+if __name__ == "__main__":
+    solution = euler_112()
+    print("e112.py: " + str(solution))
+    assert(solution == 1587000)
+

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
+