Merge pull request TheAlgorithms#96 from ZivLi/Add-bin-search-algorithm-by-recursion

Add bin-search implement by recursion

Author: AnupKumarPanwar

searches/binary_search.py

@@ -80,6 +80,39 @@ def binary_search_std_lib(sorted_collection, item):
         return index
     return None
 
+def binary_search_by_recursion(sorted_collection, item, left, right):
+
+    """Pure implementation of binary search algorithm in Python by recursion
+
+    Be careful collection must be sorted, otherwise result will be
+    unpredictable
+    First recursion should be started with left=0 and right=(len(sorted_collection)-1)
+
+    :param sorted_collection: some sorted collection with comparable items
+    :param item: item value to search
+    :return: index of found item or None if item is not found
+
+    Examples:
+    >>> binary_search_std_lib([0, 5, 7, 10, 15], 0)
+    0
+
+    >>> binary_search_std_lib([0, 5, 7, 10, 15], 15)
+    4
+
+    >>> binary_search_std_lib([0, 5, 7, 10, 15], 5)
+    1
+
+    >>> binary_search_std_lib([0, 5, 7, 10, 15], 6)
+
+    """
+    midpoint = left + (right - left) // 2
+
+    if sorted_collection[midpoint] == item:
+        return midpoint
+    elif sorted_collection[midpoint] > item:
+        return binary_search_by_recursion(sorted_collection, item, left, right-1)
+    else:
+        return binary_search_by_recursion(sorted_collection, item, left+1, right)
 
 def __assert_sorted(collection):
     """Check if collection is sorted, if not - raises :py:class:`ValueError`