poj 3020 Antenna Placement

此题的关键是在于构建二分图，可以先把每个‘*’筛出来，并编号，然后用上下左右的方式查找附近的‘×’，查找成功后存入City[Map[i][j]][Map[x][y]] = true,然后进入用二分图搜索就可以了，反正是模板，记住就可以，多大几次就懂了

Description

The Global Aerial Research Centre has been allotted the task of building the fifth generation of mobile phone nets in Sweden. The most striking reason why they got the job, is their discovery of a new, highly noise resistant, antenna. It is called 4DAir, and comes in four types. Each type can only transmit and receive signals in a direction aligned with a (slightly skewed) latitudinal and longitudinal grid, because of the interacting electromagnetic field of the earth. The four types correspond to antennas operating in the directions north, west, south, and east, respectively. Below is an example picture of places of interest, depicted by twelve small rings, and nine 4DAir antennas depicted by ellipses covering them.

Obviously, it is desirable to use as few antennas as possible, but still provide coverage for each place of interest. We model the problem as follows: Let A be a rectangular matrix describing the surface of Sweden, where an entry of A either is a point of interest, which must be covered by at least one antenna, or empty space. Antennas can only be positioned at an entry in A. When an antenna is placed at row r and column c, this entry is considered covered, but also one of the neighbouring entries (c+1,r),(c,r+1),(c-1,r), or (c,r-1), is covered depending on the type chosen for this particular antenna. What is the least number of antennas for which there exists a placement in A such that all points of interest are covered?

Input

On the first row of input is a single positive integer n, specifying the number of scenarios that follow. Each scenario begins with a row containing two positive integers h and w, with 1 <= h <= 40 and 0 < w <= 10. Thereafter is a matrix presented, describing the points of interest in Sweden in the form of h lines, each containing w characters from the set ['*','o']. A '*'-character symbolises a point of interest, whereas a 'o'-character represents open space.

Output

For each scenario, output the minimum number of antennas necessary to cover all '*'-entries in the scenario's matrix, on a row of its own.

Sample Input

2
7 9
ooo**oooo
**oo*ooo*
o*oo**o**
ooooooooo
*******oo
o*o*oo*oo
*******oo
10 1
*
*
*
o
*
*
*
*
*
*

Sample Output

17
5

#include <iostream>
#include <cstdio>
#include <cstring>

using namespace std;

int Map[44][14];
bool City[440][440];
int Link[440];
bool vis[440];
int id;
int n,m;
int ant;
int Dir[][2] = {{1,0},{-1,0},{0,1},{0,-1}};

bool DFS(int x)
{
    for(int i=1; i<=id; i++)
    {
        if(City[x][i] && !vis[i])
        {
            vis[i] = true;
            if(Link[i] == 0 || DFS(Link[i]))
            {
                Link[i] = x;
                return true;
            }
        }
    }
    return false;
}
void Search()
{
    for(int i=1; i<=id; i++)
    {
        memset(vis,false,sizeof(vis));
        if(DFS(i))
            ant++;
    }
    return ;
}
int main()
{
    //freopen("in.txt","r",stdin);
    int T;
    char str[44][14];
    cin>>T;
    while(T--)
    {
        memset(Link,0,sizeof(Link));
        memset(Map,0,sizeof(Map));
        memset(City,false,sizeof(City));
        id = 0;
        ant = 0;
        cin>>n>>m;
        for(int i=1; i<=n; i++)
        {
            for(int j=1; j<=m; j++)
            {
                cin>>str[i][j];
                if(str[i][j] == '*')
                {
                    Map[i][j] = ++id;
                }
            }
        }

        for(int i=1; i<=n; i++)
        {
            for(int j=1; j<=m; j++)
            {
                if(Map[i][j])
                {
                    for(int k=0; k<4; k++)
                    {
                        int x = Dir[k][0] + i;
                        int y = Dir[k][1] + j;
                        if(Map[x][y])
                        {
                            City[Map[i][j]][Map[x][y]] = true;
                        }
                    }
                }

            }
        }
        Search();
        printf("%d\n",id - ant/2);

    }
    return 0;
}