23longest-consecutive-sequence

题目描述

给定一个无序的整数类型数组，求最长的连续元素序列的长度。

例如：

给出的数组为[100, 4, 200, 1, 3, 2],

最长的连续元素序列为[1, 2, 3, 4]. 返回这个序列的长度：4

你需要给出时间复杂度在O（n）之内的算法

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

For example,
Given[100, 4, 200, 1, 3, 2],
The longest consecutive elements sequence is[1, 2, 3, 4]. Return its length:4.

Your algorithm should run in O(n) complexity.

示例1

输入

复制

[100, 4, 200, 1, 3, 2]

输出

复制

4

class Solution {
public:
    /**
     * 
     * @param num int整型vector 
     * @return int整型
     */
    int longestConsecutive(vector<int>& num) {
        // write code here
        set<int> Set(num.begin(),num.end());
        int result=1;
        for (int x:num)
        {
            if (Set.find(x)==Set.end())
                continue;
            Set.erase(x);
            int l=x-1,r=x+1;
            while (Set.find(l)!=Set.end())
                Set.erase(l--);
            while (Set.find(r)!=Set.end())
                Set.erase(r++);
            result=max(result,r-l-1);
            
        }
        return result;
    }
    
};