Moved more problems to Python.

python/lib_misc.py

@@ -1,3 +1,6 @@
+from functools import lru_cache
+
+
 def get_digits_reversed(n):
     """
     Returns a list of digits for n.
@@ -76,3 +79,59 @@ def product(l):
     from functools import reduce
     import operator
     return reduce(operator.mul, l, 1)
+
+
+def triangle_numbers():
+    c = 0
+    i = 1
+    while True:
+        c += i
+        yield c
+        i += 1
+
+
+def even(n):
+    """
+    Returns true if a number is even.
+    """
+    return n % 2 == 0
+
+
+def odd(n):
+    """
+    Returns true if a number is odd.
+    """
+    return n % 2 != 0
+
+
+def collatz_sequence(n):
+    """
+    Returns collatz sequence for n.
+
+    :param n: collatz sequence
+    """
+    cs = []
+    while n != 1:
+        cs.append(n)
+        n = n // 2 if n % 2 == 0 else 3 * n + 1
+    cs.append(n)
+    return cs
+
+
+@lru_cache(maxsize=1000000)
+def collatz_sequence_length(n):
+    """
+    Returns length of collatz sequence for n.
+
+    :param n: collatz sequence
+    """
+    if n == 1:
+        return 1
+    length = 1
+    while odd(n):
+        n = 3 * n + 1
+        length += 1
+    return length + collatz_sequence_length(n // 2)
+
+
+