[Leetcode]

Problem Description:

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.

Basic ideas:

The key that takes advantage of the map is the knowledge of sorting, inserting an array into the map, and then counting the longest lenth.

Code:

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]