#Leetcode# 128. Longest Consecutive Sequence

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

Given an unsorted array of integers, find the length of the longest consecutive elements sequence.

Your algorithm should run in O(n) complexity.

Example:

Input: [100, 4, 200, 1, 3, 2]
Output: 4
Explanation: The longest consecutive elements sequence is [1, 2, 3, 4]. Therefore its length is 4.

代码：

class Solution {
public:
    int longestConsecutive(vector<int>& nums) {
        if(nums.empty()) return 0;
        sort(nums.begin(), nums.end());
        set<int> s;
        int n = nums.size();
        if(n == 1) return 1;
        int ans = 1;
        for(int i = 0; i < n; i ++) {
            int temp = i;
            while(temp < n - 1 && (nums[temp] == nums[temp + 1] || nums[temp] + 1 == nums[temp + 1])) {
                s.insert(nums[temp]);
                temp ++;
            }
            s.insert(nums[temp]);
            ans = max(ans, (int)s.size());
            s.clear();
            i = temp;
        }
        return ans;
    }
};

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