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;}