学步园

题目地址：点击打开链接

就是普通的回溯就可以了

#include <iostream>
#include <cstring>
using namespace std;
int graph[30][30];
int n;
int max_num;
void dfs(int num,int sum)
{
	for(int i=0;i<n;++i)
	{
		if(graph[num][i]!=0)
		{
			graph[num][i]=graph[i][num]=0;
			++sum;
			if(sum>max_num)
				max_num=sum;
			dfs(i,sum);
			--sum;
			graph[num][i]=graph[i][num]=1;
		}
	}
}
int main()
{
	int m;
	while(cin>>n>>m)
	{
		if(n==0&&m==0)
			break;
		memset(graph,0,sizeof(graph));
		for(int i=0;i<m;++i)
		{
			int a,b;
			cin>>a>>b;
			graph[a][b]=graph[b][a]=1;
		}
		max_num=-1;
		for(int i=0;i<n;++i)
			dfs(i,0);
		cout<<max_num<<endl;
	}
	return 0;
}