Leetcode 128. Longest Consecutive Sequence

https://leetcode.com/problems/longest-consecutive-sequence/description/
学到的新的data structure：
unordered_set
http://www.cplusplus.com/reference/unordered_set/unordered_set/
unordered_set和unordered_map内部实现是基于哈希表(hashtable)
在一个unordered_set内部，元素不会按任何顺序排序。

class Solution {
public:
    int longestConsecutive(vector<int>& nums) {
        unordered_set<int>numset(nums.begin(), nums.end());
        int res = 0;
        for(auto num : nums)
        {
            if(numset.find(num) == numset.end()) continue;
            numset.erase(num);
            int pre = num - 1;
            int post = num + 1;
            while(numset.find(pre) != numset.end())
            {
                numset.erase(pre);
                pre--;
            }
            while(numset.find(post) != numset.end())
            {
                numset.erase(post);
                post++;
            }
            
            res = max(post - pre - 1, res);
        }
        return res;
    }
};