two |= one & nums[i] 
one ^= nums[i]       #新来的为0，one不变，新来为1时，one是0、1交替改变
three = one & two    #当one和two为1是，three为1（此时代表要把one和two清零了）
one &= ~three        #把one清0
two &= ~three        #把two清0

public int singleNumber(int[] A) {
    int ones = 0, twos = 0;
    for(int i = 0; i < A.length; i++){
        ones = (ones ^ A[i]) & ~twos;
        twos = (twos ^ A[i]) & ~ones;
    }
    return ones;
}