剑指 Offer 56 - II. 数组中数字出现的次数 II

class Solution {
    public int singleNumber(int[] nums) {
        int[] bitCount = new int[32];

        for (int num : nums) {
            for (int i = 0; i < 32; i++) {
                bitCount[i] += num & 1;
                num >>= 1;
            }
        }

        int num = 0;
        for (int i = 0; i < 32; i++) {
            if (bitCount[i] % 3 != 0) {
                num |= (1 << i);
            }
        }

        return num;
    }
}

Reference