题目描述：

https://leetcode.com/problems/longest-consecutive-sequence/

Code:

//mycode
class Solution {
public:
    int longestConsecutive(vector<int>& nums) {
        set<int> tp_st( nums.begin() , nums.end() );
        vector<int> tp_nums( tp_st.begin(), tp_st.end() );
        if( tp_nums.size() != 0){
            int maxlength = 1;
            int begin = 0 ;
            sort(tp_nums.begin(), tp_nums.end());
            for (int i = 0; i < tp_nums.size() -1 ; i++) {
                if (tp_nums.at(i+1) != tp_nums.at(i) + 1) {
                    int tp_len = i - begin + 1;
                    if (tp_len > maxlength) {
                        maxlength = tp_len;
                    }
                    begin = i + 1;
                }
            }
            int tp_len = tp_nums.size() - begin ;
            if (tp_len > maxlength) {
                maxlength = tp_len;
            }
            return maxlength;
        }else{
            return 0;
        }
    }
};
//other people's good solution

class Solution {
public:
    int longestConsecutive(vector<int>& nums) {
        int res = 0;
        unordered_map<int, int> m;
        for (int d : nums) {
            if (!m.count(d)) {
                int left = m.count(d - 1) ? m[d - 1] : 0;
                int right = m.count(d + 1) ? m[d + 1] : 0;
                int sum = left + right + 1;
                m[d] = sum;
                res = max(res, sum);
                m[d - left] = sum;
                m[d + right] = sum;
            }
        }
        return res;
    }
};