LeetCode Longest Consecutive Sequence

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.