CODE 134. Single Number II

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Given an array of integers, every element appears three times except for one. Find that single one.
Note:
Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?

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

	return ones;
}