uva539(卡坦岛）-回溯法

#include<stdio.h>
#include<string.h>
int map[26][26],vis[26][26];
int n,m,pathmax;
void dfs(int i,int d)
{
	if(d>pathmax) pathmax=d;
	for(int j=0;j<n;j++)
	{
		if(!vis[j][i]&&!vis[i][j]&&map[i][j]&&i!=j)
		{
			vis[i][j]=vis[j][i]=1;
			dfs(j,d+1);
			vis[i][j]=vis[j][i]=0;
		}
	}
}
int main()
{
	int i,x,y;
	while(scanf("%d%d",&n,&m)==2&&n&&m)
	{
		memset(map,0,sizeof(map));
		for(i=0;i<m;i++)
		{
			scanf("%d%d",&x,&y);
			map[x][y]=map[y][x]=1;
		}
		pathmax=0;
		for(i=0;i<n;i++)
		{
			memset(vis,0,sizeof(vis));
			dfs(i,0);
		}
		printf("%d\n",pathmax);
	}
	return 0;
}