joj 1066

 1066: Fire Net II

Result	TIME Limit	MEMORY Limit	Run Times	AC Times	JUDGE
	3s	8192K	612	241	Standard

1st JOJ Cup Online VContest Warmup Problem

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 eight openings through which to shoot. The eight openings are facing North, Northeast, East, Southeast, South, Southwest, West and Northwest, 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, vertical column and diagonal line in a map unless there is at least one wall separating them. In this problem we will consider small square cities (at most 8x8) 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 4; 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.

Input Specification

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 8. 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 Specification

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
XXX.
..X.
2
XX
.X
3
.X.
X.X
.X.
3
...
.XX
.XX
8
........
........
........
........
........
........
........
........
0

Sample Output

4
1
2
2
8

This problem is used for contest: 150 

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这是一个搜索的题从八个方向进行搜索

#include<cstdio>

char map[10][10];
int max;
bool ok(int u,int v,int n)
{
    if(map[u][v]=='X')return false;
    //向左
    for(int i=v-1;i>=1&&map[u][i]!='X';i--)
    {
        if(map[u][i]=='*')return false;
    }
    //向上
    for(int i=u-1;i>=1&&map[i][v]!='X';i--)
    {
        if(map[i][v]=='*')return false;
    }
    //左上
    for(int i=u-1,j=v-1;i>=1&&j>=1&&map[i][j]!='X';i--,j--)
    {
        if(map[i][j]=='*')return false;
    }
    //右上
    for(int i=u-1,j=v+1;i>=1&&j<=n&&map[i][j]!='X';i--,j++)
    {
        if(map[i][j]=='*')return false;
    }
    return true;
}
void dfs(int u,int v,int set,int n)
{
    if(v==n+1){v=1;u++;}
    if(u==n+1){max=max>set?max:set;return ;}
    if(ok(u,v,n))
    {
        map[u][v]='*';
        dfs(u,v+1,set+1,n);
        map[u][v]='.';
    }
    dfs(u,v+1,set,n);
}
int main()
{
    freopen("in.txt","r",stdin);
    freopen("out.txt","w",stdout);
    int n;
    while(scanf("%d",&n),n)
    {
        max=0;
        getchar();
        for(int i=1;i<=n;i++)
        {
            gets(map[i]+1);
        }
        for(int i=1;i<=n;i++)
        dfs(1,1,0,n);
        printf("%d\n",max);
    }
    return 0;
}