题目：

题解：

class Solution {
public:int longestConsecutive(vector<int>& nums) {unordered_set<int> num_set;for (const int& num : nums) {num_set.insert(num);}int longestStreak = 0;for (const int& num : num_set) {if (!num_set.count(num - 1)) {int currentNum = num;int currentStreak = 1;while (num_set.count(currentNum + 1)) {currentNum += 1;currentStreak += 1;}longestStreak = max(longestStreak, currentStreak);}}return longestStreak;           }
};