leetcode128 Longest Consecutive Sequence

思路：

维护一个unordered_map，key是每个连续区间的端点，value是该区间的长度。

实现：

 class Solution
 {
 public:
     int longestConsecutive(vector<int>& nums)
     {
         unordered_map<int, int> mp;
         int ans = ;
         for (auto it: nums)
         {
             if (mp.count(it)) continue;
             int l = mp.count(it - ) ? mp[it - ] : ;
             int r = mp.count(it + ) ? mp[it + ] : ;
             int sum = l + r + ;
             ans = max(ans, sum);
             mp[it] = sum;
             mp[it - l] = sum;
             mp[it + r] = sum;
         }
         return ans;
     }
 };