Added implementation of exponential search

Author: OmkarPathak

pygorithm/searching/exponential_search.py

@@ -0,0 +1,74 @@
+"""
+Author: OMKAR PATHAK
+Created On: 26th August 2017
+
+ - Best O(1)
+ - Average O(logn)
+ - Worst O(logn)
+
+ More info: https://en.wikipedia.org/wiki/Exponential_search
+"""
+
+from __future__ import division
+import inspect
+
+def binary_search(_list, left, right, target):
+    if right >= left:
+        mid = (left + right) // 2
+
+        # if element is present at the mid itself
+        if _list[mid] == target:
+            return mid
+
+        # If the element is smaller than mid, then it
+        # can only be present in the left subarray
+        if _list[mid] > target:
+            return binary_search(_list, left, mid - 1, target)
+
+        # Else the element can only be present in the right
+        return binary_search(_list, mid + 1, right, target)
+
+    return False
+
+def search(_list, target):
+    """
+    This function performs a exponential search
+    on a sorted list and returns the index
+    of item if successful else returns False
+
+    :param _list: list to search
+    :param target: item to search for
+    :return: index of item if successful else returns False
+    """
+
+    if type(_list) is not list:
+        raise TypeError("Exponential search only excepts lists, not {}".format(str(type(_list))))
+
+    # is target is at the first position itself
+    if _list[0] == target:
+        return 0
+
+    # Find range for binary seaarch by repeated doubling
+    i = 1
+    while i < len(_list) and _list[i] <= target:
+        i = i * 2
+
+    return binary_search(_list, i//2, min(i, len(_list)), target)
+
+
+def time_complexities():
+    """
+    Return information on functions
+    time complexity
+    :return: string
+    """
+    return "Best Case: O(1), Average Case: O(logn), Worst Case: O(logn)"
+
+
+def get_code():
+    """
+    easily retrieve the source code
+    of the function
+    :return: source code
+    """
+    return inspect.getsource(search)