Fire Net Java程序

题目：

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.

 

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.

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.

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..
....
XX..
....
2
XX
.X
3
.X.
X.X
.X.
3
...
.XX
.XX
4
....
....
....
....
0

Sample output:

5
1
5
2
4

java代码：

import java.util.Scanner;


public class Main {
    public static int  max = 0;
    
    public static void main(String[]args)
    {
        readInput();
    }
    
    /**
     * 打印最大值
     * @param square
     */
    public static void calculate(char[][] square)
    {
        int[][] layout = initLayout(square);        
        
        max = 0;
        
        calLayout(layout,0);
        
        System.out.println(max);
    }
    
    /**
     * 尝试各种建造方案
     * @param layout
     * @param location
     */
    private static void calLayout(int[][]layout,int location)
    {
        int rowSize = layout.length;
        int columnSize = layout[0].length;

        for(int current = location;current <rowSize * columnSize;current++ )
        {
            int rowIndex = current/columnSize;
            int columnIndex = current%columnSize;
            if(isBuild(layout,rowIndex,columnIndex))
            {                    
                layout[rowIndex][columnIndex] = 1;
                calLayout(layout,current+1);
                layout[rowIndex][columnIndex] = 0;
                calLayout(layout,current+1);                
            }
        }
        int count = calculateCount(layout);
        if(count > max)
        {
            max = count;
        }
    
    }
    
    /**
     * 计算当前最大碉堡数
     * @param layout
     * @return
     */
    public static int calculateCount(int[][] layout)
    {
        int count = 0;
        for(int i = 0; i < layout.length;i++)
        {
            for(int j = 0; j < layout[0].length;j++)
            {
                if(layout[i][j] == 1)
                {
                    count++;
                }
            }
        }    
        return count;
    }
    
    /**
     * 判断当前位置是否能建造
     * @param layout
     * @param rowIndex
     * @param columnIndex
     * @return
     */
    public static boolean isBuild(int[][] layout,int rowIndex,int columnIndex)
    {
        if(layout[rowIndex][columnIndex] == -1)
        {
            return false;
        }
        boolean rowAccess = true;
        boolean columnAccess = true;
        
        int rowSize = layout.length;
        int columnSize = layout[0].length;
        
        int rowFlag = 0;
        for(int i = 0; i < columnSize;i++)
        {
            if(i == columnIndex)
            {
                rowFlag ++;
            }
            else
            {
                rowFlag += layout[rowIndex][i];
            }
            
            if(rowFlag >=2)
            {
                rowAccess = false;
                break;
            }        
        }
        
        int columnFlag = 0;
        for(int i = 0; i < rowSize;i++)
        {
            if(i == rowIndex)
            {
                columnFlag ++;
            }
            else
            {
                columnFlag += layout[i][columnIndex];
            }
            
            if(columnFlag >=2)
            {
                columnAccess = false;
                break;
            }        
        }
        
        return rowAccess&&columnAccess;
    }
    
    /**
     * 初始化布局（'.':0,'X':-1,其他：-1）
     * @param square
     * @return
     */
    private static int[][] initLayout(char[][] square) {
        int rowSize = square.length;
        int columnSize = square[0].length;
        int[][] layout = new int[rowSize][columnSize];
        for(int i = 0;i < rowSize;i++)
        {
            for(int j = 0;j < columnSize;j++)
            {
                switch(square[i][j])
                {
                    case '.':
                        layout[i][j] = 0;
                        break;
                    case 'X':
                        layout[i][j] = -1;
                        break;
                    default:
                        layout[i][j] = -1;                
                }
            }
        }
        return layout;
    }

    /**
     * 读取输入
     */
    public static void readInput()
    {
        char[][] square = null;;
        Scanner scanner = new Scanner(System.in);
        int size;
        while((size = scanner.nextInt()) != 0)
        {
            square = new char[size][size];
            scanner.nextLine();
            for(int i = 0;i < size;i++)
            {                
                String line = scanner.nextLine();
                char[] charArray = line.toCharArray();
                for(int j = 0;j < Math.min(charArray.length,size);j++)
                {
                    square[i][j] = charArray[j];
                }
                
            }
            calculate(square);
        }        
    }

}