public int singleNumber1(int[] A) {
		if(A == null || A.length == 0) return 0;
		int res = 0, mark = 0;
		
		while(mark < 32) {
			int temp = checkBit(A, mark);
			if(temp == 1) res += (1 << mark);
			else if(temp == -1) break;
			mark++;
		}
	
		return res;
	}