POJ 1101

#include <iostream>
#include <string>
#define MAXN 78
#define min _min 
#define inf 123456789
using namespace std;

char _m[MAXN][MAXN];
bool mark[MAXN][MAXN];
int dp[MAXN][MAXN];
int dis[4][2] = {0,1,0,-1,1,0,-1,0};
int dis_mark[4] = {4,3,2,1};
int min;
int x_2;
int y_2;
int real_w;
int real_h;
void dfs(int x,int y,int dir,int step);
int main()
{
    //freopen("acm.acm","r",stdin);
//    freopen("out.txt","w",stdout);
    int w;
    int h;
    int i;
    int j;
    int x_1;
    int y_1;
    int temp_x;
    int temp_y;
    string s;
    int time = 0;
    while(cin>>w>>h,w||h)
    {
        cout<<"Board #"<<++ time<<":"<<endl;
        getchar();
        int time_in = 0;
        real_w = w+2;
        real_h = h+2;
        memset(_m,' ',sizeof(_m));
        for(i = 1; i <= h; ++ i)
        {
            getline(cin,s);
            for(j = 1; j <= w; ++ j)
            {
                _m[i][j] = s[j-1];    
            }
        }
    
        
        while(cin>>y_1>>x_1>>y_2>>x_2,x_1||y_1||x_2||y_2)
        {
            
            cout<<"Pair "<<++ time_in<<": ";
            memset(mark,false,sizeof(mark));
            for(i = 0; i < MAXN; ++ i)
            {
                for(j = 0; j < MAXN; ++ j)
                {
                    dp[i][j] = inf;
                }
            }
            min = inf;
            for(i = 0; i < 4; ++ i)
            {
                temp_x = x_1 + dis[i][0];
                temp_y = y_1 + dis[i][1];
                if((_m[temp_x][temp_y] != 'X' ||_m[temp_x][temp_y] == 'X' && temp_x == x_2 && temp_y == y_2) && !mark[temp_x][temp_y])
                {
                    mark[temp_x][temp_y] = true;
                    dfs(temp_x,temp_y,dis_mark[i],1);
            
                    mark[temp_x][temp_y] = false;
                }
            }
            if(min == inf)
            {
                cout<<"impossible."<<endl;
            }
            else
            {
                cout<<min;
                cout<<" segments."<<endl;
            }
        }
        cout<<endl;
    }
}
//上 1  
//下 2
//左 3
//右 4
void dfs(int x,int y,int dir,int step)
{
    if(x == x_2 && y == y_2)
    {
        if(step < min)
        {
            min = step;
        }
        return;
    }

    if(step < dp[x][y])
    {
        dp[x][y] = step;
    }
    else
    {
        return;
    }

    int i;
    int j;
    int temp_x;
    int temp_y;// 右
    for(i = 0; i < 4; ++ i)
    {
        temp_x = dis[i][0] + x;
        temp_y = dis[i][1] + y;
        if(temp_x >= 0 && temp_x < real_h && temp_y >= 0 && temp_y <= real_w &&( _m[temp_x][temp_y] != 'X' || _m[temp_x][temp_y] == 'X' && temp_x == x_2 && temp_y == y_2)&& !mark[temp_x][temp_y])
        {
            mark[temp_x][temp_y] = true;
            if(dis_mark[i] != dir)
            {
                dfs(temp_x,temp_y,dis_mark[i],step+1);
                if(step+1 < dp[temp_x][temp_y])
                    dp[temp_x][temp_y] = step+1;
            }
            else
            {
                dfs(temp_x,temp_y,dis_mark[i],step);
                if(step < dp[temp_x][temp_y])
                    dp[temp_x][temp_y] = step;
            }
            mark[temp_x][temp_y] = false;
        }
    }

}

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