Easy solution

```
public class Solution {
public int findComplement(int num) {
return Integer.parseInt(Integer.toBinaryString(num).replace("0","2").replace("1","0").replace("2","1"),2);
}
}
```

Steps:

1)num = 5

2)toBinaryString = 101 //convert in binary string

3)replace("0","2") = 121 //is possible use any letter or number

4)replace("1","0") = 020

5)replace("2","1") = 010

6)parseint("010",2) = 2 //convert to int using base 2