字符串算法——單一數(Single Number II)

問題：
Given an array of integers, every element appears three times except for one, which appears exactly once. Find that single one.

Note:
Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?
給定一個整數數組，每個元素都出現三次，除了一個元素只出現過一次，找到那個單一數。
思路一：不考慮附加條件，可以採用暴力方法，依次對每個算法進行比較
思路二：採用異或的方法

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

對於出現奇數次的該類方法都可以用該方法。