- Basically get the len of the binary representation of that string.
- Make 1's of that and subtract the number from that

E.g. 5 -> 101. Subtract from 111 and we get 010.

1 -> 1. Subtact from 1 and we get 0

```
def findComplement(self, num):
"""
:type num: int
:rtype: int
"""
allOnes = '1' * (len(bin(num)) -2)
return int(allOnes, 2) - num
```