POJ 3020 - Antenna Placement

B - Antenna Placement

Time Limit:1000MS     Memory Limit:65536KB     64bit IO Format:%I64d & %I64u

Submit Status Practice POJ 3020

Appoint description: System Crawler  (2016-01-09)

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

27 9ooo**oooo**oo*ooo*o*oo**o**ooooooooo*******ooo*o*oo*oo*******oo10 1***o******

Sample Output

175

一个城市发出的信号可以覆盖与它上下左右相邻的其中一个城市，求至少多少个城市发出信号才能使所有城市都有信号覆盖。二分图匹配，集合是城市的集合，求最小路径覆盖。注意是无向图，匹配数要除以2

#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>#include <map>using namespace std;#define H 45#define W 15struct node{int x,y;bool operator < (const node &node) const{return x==node.x?y<node.y:x<node.x;}node(int xx,int yy):x(xx),y(yy){}};int num;char a[H][W];int g[H*W][H*W];int vis[H*W];int last[H*W];int h,w;int vx[]={0,0,1,-1};int vy[]={1,-1,0,0};bool check(int x,int y){if (x<0 && x>=h)return false;if (y<0 && y>=w)return false;return true;}bool find(int u){for (int v=0;v<num;v++){if (g[u][v] && !vis[v]){vis[v]=1;if (last[v]==-1 || find(last[v])){last[v]=u;return true;}}}return false;}int solve(){map<node,int> m;scanf("%d%d",&h,&w);num=0;for (int i=0;i<h;i++){getchar();for (int j=0;j<w;j++){a[i][j]=getchar();if (a[i][j]=='*'){m[node(i,j)]=num++;//cout<<i<<' '<<j<<' '<<num<<endl;}}}memset(g,0,sizeof(g));for (int i=0;i<h;i++){for (int j=0;j<w;j++){if (a[i][j]=='*'){for (int k=0;k<4;k++){int tx=i+vx[k];int ty=j+vy[k];if (check(tx,ty) && a[tx][ty]=='*')g[m[node(i,j)]][m[node(tx,ty)]]=1;}}}}//for (int i=0;i<num;i++){//for (int j=0;j<num;j++)//cout<<g[i][j];//cout<<endl;//}int ret=0;memset(last,-1,sizeof(last));for (int i=0;i<num;i++){memset(vis,0,sizeof(vis));if (find(i))ret++;}return num-ret/2;}int main(){int n;scanf("%d",&n);while (n--){printf("%d\n",solve());}return 0;}