zoj 1002 Fire Net【DFS】

Fire Net

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Time Limit: 2 Seconds      Memory Limit: 65536 KB

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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 islegal 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 integern 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......2XX.X3.X.X.X.X.3....XX.XX4................0

Sample output:

51524

嗯，题目大意就是说，'X'为墙，'.'为路，然后让你在'.'的地方放碉堡，但是同一行同一列不能同时有两个，但是若有墙在他们中间还是可以放的，现在给你地图，问最多放几个碉堡。说实话，这题一直都不会写，不造为啥看这题就是木耐心不想写，但不能再拖下去了，看了人家的题解，到现在，贴出来，感觉很憋屈，很不爽啊。。。

#include<cstdio>#include<cstring>int n,cnt,maxc;char mazz[8][8];int vis[8][8];int judge(int x,int y){    if(mazz[x][y]!='.')        return 0;    for(int i=0;i<x;++i)    {        if(vis[i][y])            return 0;        if(mazz[i][y]=='X')            break;    }    for(int i=x+1;i<n;++i)    {        if(vis[i][y])            return 0;        if(mazz[i][y]=='X')            break;    }    for(int i=0;i<y;++i)    {        if(vis[x][i])            return 0;        if(mazz[x][i]=='X')            break;    }    for(int i=y+1;i<n;++i)    {        if(vis[x][i])            return 0;        if(mazz[x][i]=='X')            break;    }    return 1;}void dfs(){    if(cnt>maxc)        maxc=cnt;    for(int i=0;i<n;++i)    {        for(int j=0;j<n;++j)        {            if(!vis[i][j]&&judge(i,j))            {                vis[i][j]=1;                cnt++;                dfs();                cnt--;                vis[i][j]=0;            }        }    }}int main(){    while(scanf("%d",&n)&&n)    {        maxc=cnt=0;        memset(vis,0,sizeof(vis));        for(int i=0;i<n;++i)        {            scanf("%s",mazz[i]);        }        dfs();        printf("%d\n",maxc);    }    return 0;}