double_linear_search algorithm (TheAlgorithms#2161)

* linear search iterating from both array sides

* Update double_linear_search.py

* Update double_linear_search.py

* added doctests

* updated doctests

* Update double_linear_search.py

* Update double_linear_search.py

* added blank after >>>

* made all the requested changes

* Update double_linear_search.py

* Update double_linear_search.py

Co-authored-by: Christian Clauss <cclauss@me.com>

Author: reinhold-b

searches/double_linear_search.py

@@ -0,0 +1,37 @@
+from typing import List
+
+
+def double_linear_search(array: List[int], search_item: int) -> int:
+    """
+    Iterate through the array from both sides to find the index of search_item.
+
+    :param array: the array to be searched
+    :param search_item: the item to be searched
+    :return the index of search_item, if search_item is in array, else -1
+
+    Examples:
+    >>> double_linear_search([1, 5, 5, 10], 1)
+    0
+    >>> double_linear_search([1, 5, 5, 10], 5)
+    1
+    >>> double_linear_search([1, 5, 5, 10], 100)
+    -1
+    >>> double_linear_search([1, 5, 5, 10], 10)
+    3
+    """
+    # define the start and end index of the given array
+    start_ind, end_ind = 0, len(array) - 1
+    while start_ind <= end_ind:
+        if array[start_ind] == search_item:
+            return start_ind
+        elif array[end_ind] == search_item:
+            return end_ind
+        else:
+            start_ind += 1
+            end_ind -= 1
+    # returns -1 if search_item is not found in array
+    return -1
+
+
+if __name__ == "__main__":
+    print(double_linear_search(list(range(100)), 40))