Single Number II

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?

题目大意：给定一个数组，除了一个数以外其余所有数都出现了三次，找出该数。要求事件复杂度O(N)，空间复杂度O(1)

题目难度：Medium

/**
 * Created by gzdaijie on 16/6/18
 * 记录每一个int位出现的次数,若是三的倍数,说明出现了三次
 */
public class Solution {
    public int singleNumber(int[] nums) {
        int[] tag = new int[32];
        int result = 0;

        for (int i = 0; i < 32; i++) {
            for (int j = 0; j < nums.length; j++) {
                tag[i] += (nums[j] >> i) & 1;
            }
        }
        for (int i = 0; i < 32; i++) {
            if (tag[i] % 3 != 0) result += 1 << i;
        }

        return result;
    }
}