Longest Consecutive Sequence结题报告

题目：

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.

思路：这道题只要先把各个元素放进map中，利用map的自动排序功能将元素升序排列，然后找到连续增长序列最长的长度即可，貌似set也可以，大家可以试试，以下是利用map的代码：

class Solution {
public:
    int longestConsecutive(vector<int> &num) {
        map<int,int> result;
        int n=num.size();
        for(int i=0;i<n;i++)
        result.insert(make_pair(num[i],1));
        map<int,int>::iterator iter;
        int temp=1,last,m=1;
        iter=result.begin();
        last=iter->first;
        iter++;
        for(;iter!=result.end();iter++)
        {
            if(iter->first-last==1)
            {
                temp++;
                iter->second=temp;
                if(temp>m)
                m=temp;
            }
            else
            {
                temp=1;
            }
            last=iter->first;
        }
        return m;
    }
};

这个事利用set的代码，亲测可以：

class Solution {
public:
    int longestConsecutive(vector<int> &num) {
        set<int> result;
        int n=num.size();
        for(int i=0;i<n;i++)
        result.insert(num[i]);
        set<int>::iterator iter;
        int temp=1,last,m=1;
        iter=result.begin();
        last=*iter;
        iter++;
        for(;iter!=result.end();iter++)
        {
            if(*iter-last==1)
            {
                temp++;
                if(temp>m)
                m=temp;
            }
            else
            {
                temp=1;
            }
            last=*iter;
        }
        return m;
    }
};