class Solution {

public:

    int longestConsecutive(vector<int>& nums) {

        int res = ;

        unordered_map<int,int> m;

        for(int i=;i < nums.size();i++){

            if(m.count(nums[i])) continue;

            int left = (m.count(nums[i]-) >  ? m[nums[i]-]:);

            int right = (m.count(nums[i]+) >  ? m[nums[i]+]:);

            int sum = left + right + ;

            m[nums[i]] = sum; // 为什么要加这个，不是改变两端么

            res = max(res,sum);

            m[nums[i]-left] = sum;

            m[nums[i]+right] = sum;

        }

        return res;

    }

};