ZOJ Problem Set 1002 Fire Net

http://acm.zju.edu.cn/onlinejudge/showProblem.do?problemId=2

#include <iostream>
using namespace std;

char map[5][5];
bool CanPut(char map[5][5],int x,int y)
{
	if (map[x][y]!='.')
		return false;
	for (int i=x-1;i>=0;--i)
	{
		if (map[i][y]=='F')	
			return false;
		if (map[i][y]=='X')	
			break;
	}
	for (int i=y-1;i>=0;--i)
	{
		if (map[x][i]=='F')	
			return false;
		if (map[x][i]=='X')	
			break;
	}
	return true;
}

void DFS(char map[5][5],int const N,int const step,int const put,int &max)
{
	if (max<put)
		max = put;
	if (step>=N*N)
		return;
	int x = step/N;
	int y = step%N;
	if (CanPut(map,x,y))
	{
		map[x][y]='F';
		DFS(map,N,step+1,put+1,max);
		map[x][y]='.';
	}
	DFS(map,N,step+1,put,max);
}

void ACM1002()
{
	int N;
	while(cin>>N&&N!=0)
	{
		for (int i=0;i<N;++i)
			cin>>map[i];
		int max =0;
		DFS(map,N,0,0,max);
		cout<<max<<endl;
	}
}

int main()
{
	ACM1002();
	return 0;
}