HDU 1045 Fire Net【DFS深搜】

標籤：

Fire Net Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 9880    Accepted Submission(s): 5739


Problem DescriptionSuppose that we have a square city with straight streets. A map of a city is a square board with n rows and n columns, each representing a street or a piece of wall. 

A blockhouse is a small castle that has four openings through which to shoot. The four openings are facing North, East, South, and West, respectively. There will be one machine gun shooting through each opening. 

Here we assume that a bullet is so powerful that it can run across any distance and destroy a blockhouse on its way. On the other hand, a wall is so strongly built that can stop the bullets. 

The goal is to place as many blockhouses in a city as possible so that no two can destroy each other. A configuration of blockhouses is legal provided that no two blockhouses are on the same horizontal row or vertical column in a map unless there is at least one wall separating them. In this problem we will consider small square cities (at most 4x4) that contain walls through which bullets cannot run through. 

The following image shows five pictures of the same board. The first picture is the empty board, the second and third pictures show legal configurations, and the fourth and fifth pictures show illegal configurations. For this board, the maximum number of blockhouses in a legal configuration is 5; the second picture shows one way to do it, but there are several other ways. 



Your task is to write a program that, given a description of a map, calculates the maximum number of blockhouses that can be placed in the city in a legal configuration. 
 
InputThe input file contains one or more map descriptions, followed by a line containing the number 0 that signals the end of the file. Each map description begins with a line containing a positive integer n that is the size of the city; n will be at most 4. The next n lines each describe one row of the map, with a ‘.‘ indicating an open space and an uppercase ‘X‘ indicating a wall. There are no spaces in the input file. 
 
OutputFor each test case, output one line containing the maximum number of blockhouses that can be placed in the city in a legal configuration.
 
Sample Input

4.X......XX......2XX.X3.X.X.X.X.3....XX.XX4................0

 
Sample Output

51524

 

題意：

圓圈是炮台 

黑色方塊是牆

炮台不能打穿牆

2個炮台擺放的位置不能在同一行或同一列 ，否則炮台會相互攻擊

找出在地圖上最多能放多少個炮台 

方法：深搜回溯

#include<cstdio>#include<algorithm>#include<cstring>using namespace std;int n,vis[6][6],maxx;char map[6][6];int check(int x,int y){    int i;    if(vis[x][y]!=0) return 0;    //四個方向    for(i=x-1; i>=0; i--)    {        if(vis[i][y]==1)            break;        else if(vis[i][y]==2)            return 0;    }    for(i=x+1; i<n; i++)    {        if(vis[i][y]==1)            break;        else if(vis[i][y]==2)            return 0;    }    for(i=y-1; i>=0; i--)    {        if(vis[x][i]==1)            break;        else if(vis[x][i]==2)            return 0;    }    for(i=y+1; i<n; i++)    {        if(vis[x][i]==1)            break;        else if(vis[x][i]==2)            return 0;    }    //printf("OK %d %d+",x,y);    return 1;}int DFS(int deep){    for(int i=0; i<n; i++)    {        for(int j=0; j<n; j++)        {            if(check(i,j))            {//printf("已經確認一個\n");                vis[i][j]=2;//2 炮塔                DFS(deep+1);                vis[i][j]=0;               // printf("已經刪除一個\n");            }        }    }    if(deep>maxx)        maxx=deep;    return maxx;}int main (void){    while(~scanf("%d",&n),n)    {        //memset(map,0,sizeof(map));        memset(vis,0,sizeof(vis));        getchar();        //printf("11");        for(int i=0; i<n; i++)        {            for(int ii=0; ii<n; ii++)            {                scanf("%c",&map[i][ii]);                if(map[i][ii]=='X') vis[i][ii]=1;//1 強，這裡輸成小寫x，查錯好久            }            getchar();        }        maxx=0;        printf("%d\n",DFS(0));    }    return 0;}

HDU 1045 Fire Net【DFS深搜】