class Solution {
    public int singleNumber(int[] nums) {
        int x1=0, x2=0, mask=0;
        
        for(int num:nums)
        {
            x2 ^= x1 & num;
            x1 ^= num;
            
            mask = ~(x1 & x2);
            x2 &= mask;
            x1 &= mask;
        }
        
        return x1;        
    }
}