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：

 1 class Solution
 2 {
 3 public:
 4     int longestConsecutive(vector<int>& nums) 
 5     {
 6         unordered_map<int, int> mp;
 7         int ans = 0;
 8         for (auto it: nums)
 9         {
10             if (mp.count(it)) continue;
11             int l = mp.count(it - 1) ? mp[it - 1] : 0;
12             int r = mp.count(it + 1) ? mp[it + 1] : 0;
13             int sum = l + r + 1;
14             ans = max(ans, sum);
15             mp[it] = sum;
16             mp[it - l] = sum;
17             mp[it + r] = sum;
18         }
19         return ans;
20     }
21 };