poj 1154

第一阶段未懂回溯
#include <iostream>
#include <fstream>
#include <cstring>

using namespace std;

const int MAXN=30;

char maze[MAXN][MAXN];
int vis[MAXN][MAXN];
int counter=0;
int letter[26];

void DFS(int x,int y)
{

    if(vis[x][y] || maze[x][y]=='#' || letter[maze[x][y]-65]==1)return ;

    vis[x][y]=1;
    counter++;
    letter[maze[x][y]-65]=1;

    DFS(x-1,y);
    DFS(x,y-1);
    DFS(x+1,y);
    DFS(x,y+1);
}

int main()
{
    //cout << "Hello world!" << endl;
    //freopen("input.txt","r",stdin);
    int R,C;
    while(cin>>R>>C)
        {
    memset(vis,0,sizeof(vis));
    memset(maze,'#',sizeof(maze));
    memset(letter,0,sizeof(letter));
    for(int i=1;i<=R;i++)
    {
        for(int j=1;j<=C;j++)
        {
            cin>>maze[i][j];
        }
    }
    DFS(1,1);
    cout<<counter<<endl;
    //output maze
    /*
    for(int i=0;i<=R+1;i++)
    {
        for(int j=0;j<=C+1;j++)
        {
            cout<<maze[i][j];
        }
        cout<<endl;
    }*/
    //fclose(stdin);
    }
    return 0;
}

#include <iostream>
#include <fstream>
#include <cstring>
#include <cstdio>

using namespace std;

const int MAXN=30;
char map[MAXN][MAXN];
int vis[MAXN][MAXN];
int letter[26];
int sum=1;
int total=0;
int Dir_x[4]={0,1,0,-1};
int Dir_y[4]={-1,0,1,0};
int R,C;

void DFS(int x,int y)
{
    vis[x][y]=1;
    int nextx,nexty;
    if(sum>total)total=sum;
    for(int i=0;i<4;i++)
    {
        nextx=x+Dir_x[i];
        nexty=y+Dir_y[i];
        if(nextx>=0 && nextx<R && nexty>=0 && nexty<C && !letter[map[nextx][nexty]-'A']
            && !vis[nextx][nexty])
        {
            letter[map[x][y]-'A']=1;
            sum++;
            DFS(nextx,nexty);
            sum--;
            letter[map[x][y]-'A']=0;
            vis[x][y]=0;
        }
    }

}

int main()
{
    //cout << "Hello world!" << endl;
    //freopen("input.txt","r",stdin);

    //while(scanf("%d %d",&R,&C)==2)
    cin>>R>>C;
    {
        //if(R==0 || C==0)break;

        memset(letter,0,sizeof(letter));
        memset(vis,0,sizeof(vis));
        //memset()
        for(int i=0;i<R;i++)
        {
            for(int j=0;j<C;j++)
            {
                cin>>map[i][j];
            }
        }
        DFS(0,0);
        cout<<total<<endl;
    }
    //fclose(stdin);
    return 0;
}