128. Longest Consecutive Sequence

Given an unsorted array of integers, find the length of the longest consecutive elements sequence.

Your algorithm should run in O(n) complexity.

Example:

Input: [100, 4, 200, 1, 3, 2]
Output: 4
Explanation: The longest consecutive elements sequence is [1, 2, 3, 4]. Therefore its length is 4.

class Solution {
public:
    int longestConsecutive(vector<int>& nums) {
        if(nums.size()==0) return 0;
        std::sort(nums.begin(),nums.end());
        int len = nums.size();
        int pre = nums[0];
        int current ;
        int count = 1;
        int max = count;
        for(int i=1; i<nums.size(); i++)
        {
            if(nums[i]==(pre+1))
                count++;
            else if(nums[i]>=(pre+2))
            {
                max = std::max(max, count);
                count = 1;
            }
            pre = nums[i];
        }
        max = std::max(max, count);
        return max;
    }
};