Description

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

Note

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

Example

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.

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.
 

Solution

我們先使用Integer.highestOneBit方法得到數字的二進位制的最高位，例如，對於二進位制00000000 01100011通過這個方法將會得到00000000 01000000，將其左移並減一得到00000000 01111111，這串掩碼可以用來消除開頭的0待會取反碼轉成1的位。然後我們將原數字取反碼得到11111111 10011100，再與剛才的掩碼相與便得到捨棄了不必要的高位取反的最終答案00000000 00011100。

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