LeetCode-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.

unordered_set是C++自带的hash表

class Solution {
public:
    int longestConsecutive(vector<int> &num) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(num.size()==0)return 0;
        unordered_set<int> m;
        for(int i=0;i<num.size();i++){
            m.insert(num[i]);
        }
        int max=0;
        while(m.size()!=0){
            int v=*m.begin();
            m.erase(v);
            int i1=0,i2=0,v1=v-1,v2=v+1;
            while(m.find(v1)!=m.end()){
                m.erase(v1);
                v1--;
                i1++;
            }
            while(m.find(v2)!=m.end()){
                m.erase(v2);
                v2++;
                i2++;
            }
            int length=i1+i2+1;
            if(length>max){
                max=length;
            }
        }
        return max;
    }
};