leetcode(longest consecutive sequence)

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.
使用哈希表
#include<unordered_map>

#include<iostream>

#include<vector>

using namespace std;

class solution{

public:
int lc(vector<int> const&num){
unordered_map<int,bool> used;
for(auto i:num) used[i]=false;
int longest=0;
for(auto i:num)
{
if(used[i]) continue;
int length=1;
used[i]=true;
for(int j=i+1;used.find(j)!=used.end();++j)
{
used[j]=true;
++length;
}
for(int j=i-1;used.find(j)!=used.end();--j)
{
used[j]=true;
++length;
}
longest=max(longest,length);
}
return longest;
}

};

int main()

{   
vector<int> coll;
coll.push_back(200);
coll.push_back(4);
coll.push_back(100);
coll.push_back(1);
coll.push_back(3);
coll.push_back(2);
solution s;
cout<<s.lc(coll)<<endl;

}