Count number of 1's in binary representation

Question

Efficient way to count number of 1s in the binary representation of a number in O(1) if you have enough memory to play with. This is an interview question I found on an onli

Answer 1

In python or any other convert to bin string then split it with '0' to get rid of 0's then combine and get the length.

len(''.join(str(bin(122011)).split('0')))-1