1. Number Complement

Given a positive integer, output its complement number. The complement strategy is to flip the bits of its binary representation.

Note:

1. The given integer is guaranteed to fit within the range of a 32-bit signed integer.
2. You could assume no leading zero bit in the integer’s binary representation.

Example 1:

Input:
 5

Output:
 2

Explanation:
 The binary representation of 5 is 101 (no leading zero bits), and its complement is 010. So you need to output 2.

Example 2:

Input:
 1

Output:
 0

Explanation:
 The binary representation of 1 is 1 (no leading zero bits), and its complement is 0. So you need to output 0.

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Bit Manipulation

public class Solution {
    public int findComplement(int num) {
       int mask = (Integer.highestOneBit(num) << 1) - 1;
       System.out.println(mask);
       System.out.println(Integer.highestOneBit(num)-1);
       System.out.println(~num & (Integer.highestOneBit(num) - 1));
        num = ~num;
        return num & mask;
    }
}

public class Solution {
    public int findComplement(int num) {
       int m = 0;
         int n = num;
         int i = 0;
         while(n > 0){
             m += Math.pow(2, i);
             n = n>>1;
             i++;
         }
         return m - num;
    }
}