128. Longest Consecutive Sequence

class Solution {
public:
    int longestConsecutive(vector<int>& nums) {
        unordered_set<int> si;
        for(int &i: nums)
            si.insert(i);
        
        int res=0, cur=0;
        for(int i:nums){
            if(si.find(i-1)!=si.end())
                continue;
            int p=i;
            while(si.find(p)!=si.end()){
                cur++;
                p++;
            }
            res=max(res,cur);
            cur=0;
        }
        return res;
    }
};

用个哈希表来存放数组，便于查找。在查找时，只判定i-1不在哈希表中的元素为起点的连续序列