Added algorithm for finding index of rightmost set bit (#7234)

* Added algorithm for finding index of rightmost set bit

* applied suggested changes

* applied suggested changes

* Fixed failing Testcases

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Author: GautamChaurasia

bit_manipulation/index_of_rightmost_set_bit.py

@@ -0,0 +1,43 @@
+# Reference: https://www.geeksforgeeks.org/position-of-rightmost-set-bit/
+
+
+def get_index_of_rightmost_set_bit(number: int) -> int:
+    """
+    Take in a positive integer 'number'.
+    Returns the zero-based index of first set bit in that 'number' from right.
+    Returns -1, If no set bit found.
+
+    >>> get_index_of_rightmost_set_bit(0)
+    -1
+    >>> get_index_of_rightmost_set_bit(5)
+    0
+    >>> get_index_of_rightmost_set_bit(36)
+    2
+    >>> get_index_of_rightmost_set_bit(8)
+    3
+    >>> get_index_of_rightmost_set_bit(-18)
+    Traceback (most recent call last):
+        ...
+    ValueError: Input must be a non-negative integer
+    """
+
+    if number < 0 or not isinstance(number, int):
+        raise ValueError("Input must be a non-negative integer")
+
+    intermediate = number & ~(number - 1)
+    index = 0
+    while intermediate:
+        intermediate >>= 1
+        index += 1
+    return index - 1
+
+
+if __name__ == "__main__":
+    """
+    Finding the index of rightmost set bit has some very peculiar use-cases,
+    especially in finding missing or/and repeating numbers in a list of
+    positive integers.
+    """
+    import doctest
+
+    doctest.testmod(verbose=True)