Question 1. Hamming distance

• Hamming Distance - # of bits are difference from each others

  https://en.wikipedia.org/wiki/Hamming_distance

public class Solution {
    public int hammingDistance(int x, int y) {
        int cnt = 0;
        int diff = x^y;
        while(diff != 0){
            diff = diff & (diff -1);
            cnt++;
        }
        return cnt;       
    }
}

Question 2. Hamming weight

• Hamming weight- # of bits of given number

public class Solution {
    // you need to treat n as an unsigned value
    public int hammingWeight(int n) {
        int cnt = 0;
        while(n != 0){
            n = n & (n-1);
            cnt++;
        }
        return cnt;
    }
}

Question 3. Number Complement

• Update version

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

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

Question 4. power of 4

public class Solution {
    public boolean isPowerOfFour(int num) {
        return (num > 0) && ( (num & (num-1) )== 0) && ((num & 0x55555555) != 0) ;               
    }
}
/**
 * Hexademical representation
 * a: 10 , b : 11 , c : 12, d : 13, e : 14, f : 15
 * 0xa20 -> 1010 0010 0000 
 */

Question 5. find single number

*Given an array of integers, every element appears twice except for one. Find that single one.

public class Solution {
    public int singleNumber(int[] nums) {
        int res = 0;
        int i = 0;
        while(i < nums.length){
            res^=nums[i];
            i++;
        }
        return res;
    }
}
/**
 * N ^ 0 = N
 * N ^ N = 0
 */