Python/bit_manipulation/index_of_rightmost_set_bit.py

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# 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)