137. 只出现一次的数字 II

输入: [2,2,3,2]
输出: 3

输入: [0,1,0,1,0,1,99]
输出: 99

class Solution {
    public int singleNumber(int[] nums) {
        int[] bts = new int[32];
        for (int num : nums) {
            for (int i = 0; i < 32; i++) {
                bts[i] += ((num >> i) & 1);
            }
        }
        int ans = 0;
        for (int i = 0; i < 32; i++) {
            ans |= (bts[i] % 3 << i);
        }
        return ans;
    }
}

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