Create exponential_search.py

searches/exponential_search.py

@@ -0,0 +1,78 @@
+"""
+This is pure Python implementation of exponential search algorithm
+For doctests run following command:
+python3 -m doctest -v linear_search.py
+For manual testing run:
+python3 linear_search.py
+"""
+
+# A recursive binary search function returns location  of search_element in given array if present, otherwise -1
+def binary_search( array: list, left: int, right: int, search_element: int) -> int:
+    """A pure Python implementation of binary search algorithm
+    :param array: a collection with comparable items (items are sorted)
+    :param left: leftmost boundary of the array
+    :param right: rightmost boundary of the array
+    :param search_element: the element we are looking for in the array
+    :return: index of found item or -1 if item is not found
+    Examples:
+    >>> binary_search([0, 5, 7, 10, 15], 0, 4, 0)
+    0
+    >>> binary_search([0, 5, 7, 10, 15], 0, 4, 15)
+    4
+    >>> binary_search([0, 5, 7, 10, 15], 0, 4, 5)
+    1
+    >>> binary_search([0, 5, 7, 10, 15], 0, 4, 6)
+    -1
+    """
+    if right >= left:
+        middle = left + ( right-left ) // 2
+
+        # If the element is present at the middle itself
+        if array[middle] == search_element:
+            return middle
+
+        # If the element is smaller than mid, then it can only be present in the left subarray
+        if array[middle] > search_element:
+            return binary_search(array, left, 
+                                middle - 1, search_element)
+
+        # Else he element can only be present in the right
+        return binary_search(array, middle + 1, right, search_element)
+
+    # We reach here if the search_element is not present
+    return -1
+
+# Returns the position of first occurrence of search_element in array
+def exponential_search(array: list, no_of_items: int, search_element: int) -> int:
+    """A pure Python implementation of exponential search algorithm
+    :param array: a collection with comparable items (items are sorted)
+    :param no_of_items: number of items in the array
+    :param search_element: the element we are looking for in the array
+    :return: index of found item or -1 if item is not found
+    Examples:
+    >>> exponential_search([0, 5, 7, 10, 15], 5, 0)
+    0
+    >>> exponential_search([0, 5, 7, 10, 15], 5, 15)
+    4
+    >>> exponential_search([0, 5, 7, 10, 15], 5, 5)
+    1
+    >>> exponential_search([0, 5, 7, 10, 15], 5, 6)
+    -1
+    """
+
+    # IF search_element is present at first location itself
+    if array[0] == search_element:
+        return 0
+
+    index = 1
+    while index < no_of_items and array[index] <= search_element:
+        index = index * 2
+
+    # Call binary search for searching the element in the found range
+    return binary_search( array, index // 2, 
+                         min(index, no_of_items-1), search_element)
+
+
+if __name__ == "__main__":
+    import doctest
+    doctest.testmod()