476. Number Complement (E)

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: 5Output: 2Explanation: 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: 1Output: 0Explanation: 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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Solution 1:

public class Solution {    public int findComplement(int num) {        String data=Integer.toBinaryString(num);        int re=0;        int count=1;        for(int i=data.length()-1;i>=0;--i){            if(data.charAt(i)=='0')                re+=count;            count*=2;            }        return re;    }}

Solution 2:

public class Solution {    public int findComplement(int num) {        int re=0;        int count=1;        while(num!=0){            int n=num%2;            num/=2;            if(n==0)                re+=count;            count*=2;            }        return re;    }}

Disscuss Solution:

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