Update linear_search.py (#2422)

* Update linear_search.py

Python implementation of recursive linear search algorithm

* Update linear_search.py

Added different doctests
Added the parameter hints
Handled the exception

* Update linear_search.py

added parameter hints to linear_search

* Update linear_search.py

Both the functions return the index if the target is found and -1 if it is not found
The rec_linear_search raises an exception if there is an indexing problem
Made changes in the doc comments

* Update linear_search.py

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

searches/linear_search.py

@@ -2,17 +2,15 @@
 This is pure Python implementation of linear search algorithm
 
 For doctests run following command:
-python -m doctest -v linear_search.py
-or
 python3 -m doctest -v linear_search.py
 
 For manual testing run:
-python linear_search.py
+python3 linear_search.py
 """
 
 
-def linear_search(sequence, target):
-    """Pure implementation of linear search algorithm in Python
+def linear_search(sequence: list, target: int) -> int:
+    """A pure Python implementation of a linear search algorithm
 
     :param sequence: a collection with comparable items (as sorted items not required
         in Linear Search)
@@ -22,30 +20,58 @@ def linear_search(sequence, target):
     Examples:
     >>> linear_search([0, 5, 7, 10, 15], 0)
     0
-
     >>> linear_search([0, 5, 7, 10, 15], 15)
     4
-
     >>> linear_search([0, 5, 7, 10, 15], 5)
     1
-
     >>> linear_search([0, 5, 7, 10, 15], 6)
-
+    -1
     """
     for index, item in enumerate(sequence):
         if item == target:
             return index
-    return None
+    return -1
+
+
+def rec_linear_search(sequence: list, low: int, high: int, target: int) -> int:
+    """
+    A pure Python implementation of a recursive linear search algorithm
+
+    :param sequence: a collection with comparable items (as sorted items not required
+        in Linear Search)
+    :param low: Lower bound of the array
+    :param high: Higher bound of the array
+    :param target: The element to be found
+    :return: Index of the key or -1 if key not found
+
+    Examples:
+    >>> rec_linear_search([0, 30, 500, 100, 700], 0, 4, 0)
+    0
+    >>> rec_linear_search([0, 30, 500, 100, 700], 0, 4, 700)
+    4
+    >>> rec_linear_search([0, 30, 500, 100, 700], 0, 4, 30)
+    1
+    >>> rec_linear_search([0, 30, 500, 100, 700], 0, 4, -6)
+    -1
+    """
+    if not (0 <= high < len(sequence) and 0 <= low < len(sequence)):
+        raise Exception("Invalid upper or lower bound!")
+    if high < low:
+        return -1
+    if sequence[low] == target:
+        return low
+    if sequence[high] == target:
+        return high
+    return rec_linear_search(sequence, low + 1, high - 1, target)
 
 
 if __name__ == "__main__":
     user_input = input("Enter numbers separated by comma:\n").strip()
-    sequence = [int(item) for item in user_input.split(",")]
+    sequence = [int(item.strip()) for item in user_input.split(",")]
 
-    target_input = input("Enter a single number to be found in the list:\n")
-    target = int(target_input)
+    target = int(input("Enter a single number to be found in the list:\n").strip())
     result = linear_search(sequence, target)
-    if result is not None:
-        print(f"{target} found at position : {result}")
+    if result != -1:
+        print(f"linear_search({sequence}, {target}) = {result}")
     else:
-        print("Not found")
+        print(f"{target} was not found in {sequence}")