hdu 1045Fire Net(DFS or 二分匹配)

//数据小,dfs+回溯,能够水过
#include <iostream>
#include <cstring>
#include <queue>

using namespace std;
const int MAX = 10;
char map[MAX][MAX];
int n,ans;

bool can(int  x,int y)
{
    int i,j;

    for(i = x+1;i < n;++i)
    {
        if(map[i][y] == 'Z') return false;
        if(map[i][y] == 'X') break;
    }
    for(i = 0;i < x;++i)
    {
        if(map[i][y] == 'Z') return false;
        if(map[i][y] == 'X') break;
    }

    for(j = 0;j < y;++j)
    {
        if(map[x][j] == 'Z') return false;
        if(map[x][j] == 'X') break;
    }

    for(j = y+1;j < n;++j)
    {
        if(map[x][j] == 'Z') return false;
        if(map[x][j] == 'X') break;
    }

    return true;
}

void dfs(int sum)
{
    for(int i = 0;i < n;++i)
    {
        for(int j = 0;j < n;++j)
        {
            if(map[i][j] == '.' && can(i,j))
            {
                map[i][j] = 'Z';
                dfs(sum+1);
                map[i][j] = '.';
            }

            if(i == n-1 && j == n-1)
            {
                if(sum > ans) ans = sum;
                return;
            }
        }
    }
}


int main()
{
    int i;

    while(scanf("%d",&n),n != 0)
    {
        for(i = 0;i < n;++i) scanf("%s",map[i]);

        ans = -2000000;    dfs(0);

        cout<<ans<<endl;
    }

    return 0;
}