SingleNumberII.java

class Solution {
    public int singleNumber(int[] nums) {
        int ones = 0 ; //The bits that have appeared 1st time or 4th time or 7th time ... etc [We have to return this value]
        int twos = 0 ; // The bits that have appeared 2nd time or 5th time or 8th time .. etc.
        int not_threes ; //‘ones’ and ‘twos’ contain those extra bits which appear 3rd time. Removethem by finding out common set bits in ‘ones’ and ‘twos’.

        for( int x : nums )
        {
            twos |= ones & x ; //add it to twos if it exists in ones
            ones ^= x ; //if it exists in ones, remove it, otherwise, add it

            not_threes = ~(ones & twos) ;//if x is in ones and twos, dont add it to Threes.
            ones &= not_threes ;//remove x from ones
            twos &= not_threes ;//remove x from twos
        } 
      
        return ones;
        
    }
}