Added algorithm for finding index of rightmost set bit

Author: GautamChaurasia

bit_manipulation/index_of_rightmost_set_bit.py

@@ -0,0 +1,41 @@
+"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 and type(number)==int:
+        intermediate = number&~(number-1)
+        index = 0
+        while intermediate:
+            intermediate>>=1
+            index+=1
+        return index-1
+    else: raise ValueError("Input must be a non-negative integer")
+
+"""
+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.
+"""
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()