hdoj1045

你的名字 2022-08-03 11:59 38阅读 0赞

# Fire Net #

**Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)  
Total Submission(s): 7937    Accepted Submission(s): 4529**

Problem Description

Suppose 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.  
  
![1045-1.jpg][]  
  
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.

Input

The 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.

Output

For 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..           //‘X’代表墙，'.'代表空地
    ....
    XX..
    ....
    2
    XX
    .X
    3
    .X.
    X.X
    .X.
    3
    ...
    .XX
    .XX
    4
    ....
    ....
    ....
    ....
    0

Sample Output

5
    1
    5
    2
    4
      
       
      
       
    
      
       
      
       
    
      
       
      
       
    
      
       
      
       
    
      
       
      
       
        
       题目大意：
      
       
      
       
        
       在地图中，黑格子代表墙，圆点表碉堡；在同一行或同一列有且只能有一个碉堡，除非在同一行或同一列上两个碉堡之间有墙；
      
       
      
       
    
      
       
      
       
    
      
       
      
       
        
       第一行输入一个n，代表地图尺寸为n*n；当n==0时结束
      
       
      
       
        
       在接下来的n行，每行输入n个字符；
      
       
      
       
    
      
       
      
       
        
       输出：在这张地图上最多能建几个碉堡；输出独立成行；
      
       
      
       
    
      
       
      
       
    
      
       
      
       
    
      
       
      
       
       
        #include<iostream>
    using namespace std;
    int n,xam;
    char a[5][5];
    int xy(int x,int y){          //判断在当前所在的行或列有无其他碉堡，有  返回0，无  返回1；
        for(int i=x-1;i>0;i--){
            if(a[i][y]=='X') break;
            if(a[i][y]=='*') return 0;
        }
        for(int i=y-1;i>0;i--){
            if(a[x][i]=='X') break;
            if(a[x][i]=='*') return 0;
        }
        return 1;
    }
    void dfs(int x,int y,int c){
        if(x==n&&y==n){
            if(a[n][n]=='.'&&xy(n,n)) c++;
            if(xam<c) xam=c;
            return ;
        }
        if(a[x][y]=='X'||!xy(x,y)){
            if(y<n) dfs(x,y+1,c);
            else dfs(x+1,1,c);
        }
        else{
            a[x][y]='*';
            if(y<n) dfs(x,y+1,c+1);
            else dfs(x+1,1,c+1);
            a[x][y]='.';
            if(y<n) dfs(x,y+1,c);
            else dfs(x+1,1,c);    
        }
        return ;
    }
    int main(){
        int i,j;
        while(scanf("%d",&n),n){
            xam=0;
            for(i=1;i<=n;i++){
                getchar();
                for(j=1;j<=n;j++)
                    scanf("%c",&a[i][j]);
            }
            dfs(1,1,0);
            printf("%d\n",xam);
        }
        return 0;
    }

[1045-1.jpg]: /images/20220731/0659bc12a68440d0b7ba26cca9b3672e.png