Add Fibonacci Sequence Recursive Algorithm, Along with a Memoization Example

allalgorithms/numeric/__init__.py

@@ -1 +1,2 @@
-from .max_numbers import find_max
+from .max_numbers import find_max
+from .fibonacci import fibonacci, fibonacci_memo

allalgorithms/numeric/fibonacci.py

@@ -0,0 +1,44 @@
+# -*- coding: UTF-8 -*-
+#
+# Numeric Algorithms: Factorials and Memoization
+# The All ▲lgorithms library for python
+#
+# Contributed by: Chance
+# Github: @chance-nelson
+#
+
+
+def fibonacci(n):
+    """Compute the Fibonacci sequence number at a certain index
+
+    This is the obvious recursive approach, and runs on the order of O(n*2).
+    """
+    # Base case 1: fibonacci(1) == 0
+    if n == 1:
+        return 0
+
+    # Base case 2: fibonacci(2) == 1
+    elif n == 2:
+        return 1
+
+    return fibonacci(n-1) + fibonacci(n-2)
+
+
+def memoize(f):
+    """Special decorator to add memoization to any recursive function
+
+    Keep a cache of results from past runs. This cache can then be referenced
+    instead of calling the function again.
+    """
+    memory = {}
+
+    def inner(num):
+        if num not in memory:
+            memory[num] = f(num)
+
+        return memory[num]
+
+    return inner
+
+
+fibonacci_memo = memoize(fibonacci)

tests/test_numeric.py

@@ -1,6 +1,7 @@
 import unittest
 
 from allalgorithms.numeric import find_max
+from allalgorithms.fibonacci import fibonacci, fibonacci_memo
 
 
 class TestMax(unittest.TestCase):
@@ -9,5 +10,15 @@ def test_find_max_value(self):
         test_list = [3, 1, 8, 7, 4]
         self.assertEqual(8, find_max(test_list))
 
+
+class TestFibonacci(unittest.TestCase):
+
+    def test_recursive_fibonacci(self):
+        self.assertEqual(8, fibonacci(7))
+
+    def test_memoize_fibonacci(self):
+        self.assertEqual(8, fibonacci(7))
+
+
 if __name__ == "__main__":
     unittest.main()