ZOJ::1002 Fire Net

#include <iostream>
#include <memory.h>
using namespace std;

char board[6][6];                                //为4*4的城市围一圈墙，方便判断
int n;
int maxCount;

bool Shoot(int x, int y, int dx, int dy)        //x,y为射击原点；dx,dy为射击方向向量，打到堡垒返回false
{
    int x1 = x, y1 = y;
    do 
    {
        x1 += dx;
        y1 += dy;
        if (board[x1][y1] == ‘o‘)                //打到堡垒了
            return false;
    } while (board[x1][y1] != ‘X‘);                //一直打到墙
    return true;
}

bool CanPut(int x, int y)
{
    if (board[x][y] == ‘.‘ &&                    //四面各开一枪如果都没打上堡垒
        Shoot(x, y, 0, 1) &&
        Shoot(x, y, 0, -1) &&
        Shoot(x, y, 1, 0) &&
        Shoot(x, y, -1, 0))
        return true;
    return false;
}

void Slove(int k, int count) 
{
    if (k == n*n)
        maxCount = count > maxCount ? count : maxCount;
    else
    {
        int x = k % n + 1;
        int y = k / n + 1;
        if(CanPut(x, y))
        {
            board[x][y] = ‘o‘;
            Slove(k+1, count+1);                //进入分支
            board[x][y] = ‘.‘;                    //回溯
        }
        Slove(k+1, count);
    }
}

int main()
{
    while (cin >> n && n)
    {
        memset(board, ‘X‘, sizeof(board));            //载入地图
        for (int x = 1; x < n + 1; ++x)
            for (int y = 1; y < n + 1; ++y)
                cin >> board[x][y];

        maxCount = 0;
        Slove(0, 0);
        cout << maxCount <<endl;
    }
}