poj 1154 LETTERS dfs入门题

//poj 1154//sep9#include <iostream>using namespace std;const int maxR=32;char a[maxR][maxR];int r,s;int ans=1;int vis[200];void dfs(int i,int j,int len){ans=max(ans,len+1);if(i+1<r&&vis[a[i+1][j]]==0){vis[a[i+1][j]]=1;dfs(i+1,j,len+1);vis[a[i+1][j]]=0;}if(i-1>=0&&vis[a[i-1][j]]==0){vis[a[i-1][j]]=1;dfs(i-1,j,len+1);vis[a[i-1][j]]=0;}if(j+1<s&&vis[a[i][j+1]]==0){vis[a[i][j+1]]=1;dfs(i,j+1,len+1);vis[a[i][j+1]]=0;}if(j-1>=0&&vis[a[i][j-1]]==0){vis[a[i][j-1]]=1;dfs(i,j-1,len+1);vis[a[i][j-1]]=0;}}int main(){scanf("%d%d",&r,&s);for(int i=0;i<r;++i)scanf("%s",&a[i]);memset(vis,0,sizeof(vis));vis[a[0][0]]=1;dfs(0,0,0); printf("%d\n",ans);}