Longest Consecutive Sequence

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.

class Solution {

public:

    int longestConsecutive(vector<int> &num) 

    {                  

        int n=num.size();

        vector<int> v1;

        vector<int> v2;        

        for(int i=0;i<n;i++)

            if(num[i]<0) v1.push_back(num[i]);

            else v2.push_back(num[i]);

        radixsort(v1);

        radixsort(v2);

        for(int i=0;i<v1.size();i++)

            num[i]=v1[v1.size()-i-1];

        for(int i=0;i<v2.size();i++)

            num[i+v1.size()]=v2[i];

        

        //get the longest

        int longest=1;

        int index=0;

        while(true)

        {

            if(index+1>=n) break;

            int con=1;

            int index2=index;

            while(index2+1<n && (num[index2+1]==num[index2] || num[index2+1]==num[index2]+1))

            {

                if(num[index2+1]==num[index2]+1) con++;

                index2++;

            }

            if(con>longest) longest=con;

            index=index2+1;                    

        }

        return longest;

    }



    void radixsort(vector<int> &num)

    {

        int n=num.size();

        int* data=(int*)malloc(n*sizeof(int));

        int d=1;

        int radix=10;

        int* bulk=(int*)malloc(radix*sizeof(int));

        //radix sort

        for(int k=0;k<10;k++)

        {

            for(int i=0;i<radix;i++) bulk[i]=0;

            for(int i=0;i<n;i++)

            {

                int ibulk=num[i]/d%radix;

                if(ibulk<0) ibulk=-ibulk;

                bulk[ibulk]++;

            }

                

            int step=bulk[0];

            bulk[0]=0;

            for(int i=1;i<radix;i++)

            {

                int step2=bulk[i];

                bulk[i]=bulk[i-1]+step;

                step=step2;

            }

            

            for(int i=0;i<n;i++)

            {

                int ibulk=num[i]/d%radix;

                if(ibulk<0) ibulk=-ibulk;

                data[bulk[ibulk]]=num[i];

                bulk[ibulk]++;

            }



            for(int i=0;i<n;i++)

                num[i]=data[i];

                

            d=d*radix;

        }

        free(data);

        free(bulk);

    }

};