leetcode刷题，总结，记录，备忘137

leetcode137

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?
暂时没想出位操作的方法，，用的map容器，时间复杂度为O(n)，，比较简单，，直接上代码，，我去搜搜别人的解法。。。

class Solution {
public:
    int singleNumber(vector<int>& nums) {
      map<int, int> mi;
      for (vector<int>::iterator it = nums.begin(); it != nums.end(); ++it)
      {
          mi[*it]++;
      }
      
      for (map<int, int>::iterator it = mi.begin(); it != mi.end(); ++it)
      {
            if (it->second < 3)
            return it->first;
      }
    }
};