问题描述：

Given an unsorted array of integers, find the length of the longest consecutive elements sequence.

For example,
Given [100, 4, 200, 1, 3, 2],
The longest consecutive elements sequence is [1, 2, 3, 4]. Return its length:4.

Your algorithm should run in O(n) complexity.

基本思路：

本题利用了map的key是排序的知识，将array插入到map中，然后在统计最长的lenth。

代码：

int longestConsecutive(vector<int> &num) {  //C++
        map<int,int> numMap;
        for(int i = 0; i < num.size(); i++)
            numMap.insert(make_pair(num[i],num[i]));
            
        int len = 1;
        int tmp = 1;
        map<int,int>::iterator iter = numMap.begin();
        int prenum = iter->first;
        iter++;
        for(; iter!=numMap.end(); iter++)
        {
            if(iter->first - prenum == 1)
                    tmp++;
            else
            {
                if(tmp > len)
                    len = tmp;
                tmp = 1;
            }
            prenum = iter->first;
        }
        len = (len > tmp)? len:tmp;
        return len;
    }

[leetcode]