# 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.

The original problem is here.

The original code is here.

# My Solution

I solve this problem in C++, as below:

``````/*
*Longest Consecutive Sequence
*Author: shuaijiang
*Email: zhaoshuaijiang8@gmail.com
*/
#include<iostream>
#include<vector>
#include<algorithm>
#include<stdlib.h>
using namespace std;

class Solution {
public:
int longestConsecutive(vector<int>& nums) {
int longestNum = 0, num;
int size = nums.size();
if(size<=0)
return longestNum;
if(size == 1)
return 1;
sort(nums.begin(),nums.end());

longestNum = 1;
num = 1;
for(int i=1;i<size;i++){
if(nums[i]-nums[i-1] == 0)
;
else if(nums[i]-nums[i-1] == 1)
num ++;
else
num = 1;
if(num > longestNum)
longestNum = num;
}
return longestNum;
}
};
// the code under below is used for test
int main(){
Solution s;
vector<int> nums;
nums.push_back(0);
nums.push_back(-1);

int num = s.longestConsecutive(nums);
cout<<"num="<<num<<endl;
system("pause");
return 0;
}
``````

# Note

First, sort the vector. Then count the consecutive sequence, select the largest length. Note the equal number doesn’t contribute to the length.