uva 539 - The Settlers of Catan

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
const int maxn=30;

int G[maxn][maxn],vis[maxn][maxn],n,max;

void search(int u,int s)
{
	if(max<s) max=s;
	for(int v=0;v<n;v++) if(G[u][v] && !vis[u][v])
	{
		vis[u][v]=vis[v][u]=1;
		search(v,s+1);
		vis[u][v]=vis[v][u]=0;
	}
}

int main()
{
#ifndef ONLINE_JUDGE
    freopen("539.txt","r",stdin);
#endif
	int m;
	while(scanf("%d%d",&n,&m)==2 && (n || m))
	{
		int i;
		memset(G,0,sizeof(G));
		int u,v;
		for(i=0;i<m;i++)
		{
			scanf("%d%d",&u,&v);
			G[u][v]=G[v][u]=1;
		}
		max=0;
		for(i=0;i<n;i++)
		{
			memset(vis,0,sizeof(vis));
			search(i,0);
		}
		printf("%d\n",max);
	}
    return 0;
}