476.Number Complement

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Bit Manipulation, Easy

Question

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:

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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:

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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.

My Answer

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class Solution {
    public int findComplement(int num) {
        int i=0, j=0;
        while(i<num){
            i += Math.pow(2, j);
            j++;
        }
        return i-num;
    }   
}

Running time: 12ms

Better Answer

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

Running time: 11ms