HDU 1242 Rescue（BFS+優(yōu)先隊列）

題目鏈接：http://acm.hdu.edu.cn/showproblem.php?pid=1242

題面：

Rescue Time Limit: 2000/1000 MS (Java/Others)????Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 25017????Accepted Submission(s): 8862


Problem Description Angel was caught by the MOLIGPY! He was put in prison by Moligpy. The prison is described as a N * M (N, M <= 200) matrix. There are WALLs, ROADs, and GUARDs in the prison.

Angel's friends want to save Angel. Their task is: approach Angel. We assume that "approach Angel" is to get to the position where Angel stays. When there's a guard in the grid, we must kill him (or her?) to move into the grid. We assume that we moving up, down, right, left takes us 1 unit time, and killing a guard takes 1 unit time, too. And we are strong enough to kill all the guards.

You have to calculate the minimal time to approach Angel. (We can move only UP, DOWN, LEFT and RIGHT, to the neighbor grid within bound, of course.)
?
Input First line contains two integers stand for N and M.

Then N lines follows, every line has M characters. "." stands for road, "a" stands for Angel, and "r" stands for each of Angel's friend.?

Process to the end of the file.
?
Output For each test case, your program should output a single integer, standing for the minimal time needed. If such a number does no exist, you should output a line containing "Poor ANGEL has to stay in the prison all his life."?
?
Sample Input

7 8 #.#####. #.a#..r. #..#x... ..#..#.# #...##.. .#...... ........ ?
Sample Output

13 ?
Author CHEN, Xue ?
Source ZOJ Monthly, October 2003 ? 解題：

? ? 從a出發(fā)去找r，用優(yōu)先隊列，當前cost值小的，優(yōu)先級高，只要找到一個r就可以結束了。

代碼：

#include 
#include 
#include 
#include 
#include 
#include 
#define eps 1e-8
#define LL long long
using namespace std;
int n,m,ans,dir[4][2]={0,-1,-1,0,0,1,1,0};
char mapp[202][202];
bool vis[202][202];
struct step
{
	int x,y,cost;
	bool operator <(const step &b)const
	{
		return cost>b.cost;
	}
};
priority_queue  qe;
void bfs(int x,int y)
{
	while(!qe.empty())
	  qe.pop();
	int tx,ty;
	step tmp,cur;
	tmp.x=x;
	tmp.y=y;
	tmp.cost=0;
	qe.push(tmp);
	while(!qe.empty())
	{
		cur=qe.top();
		qe.pop();
		for(int i=0;i<4;i++)
		{
			tx=cur.x+dir[i][0];
			ty=cur.y+dir[i][1];
			if(tx>=1&&tx<=n&&ty>=1&&ty<=m&&!vis[tx][ty])
			{
				if(mapp[tx][ty]=='r')
				{
					vis[tx][ty]=1;
					  ans=cur.cost+1; 
			        return; 
				}
				else if(mapp[tx][ty]=='x')
				{
					tmp.x=tx;
					tmp.y=ty;
					tmp.cost=cur.cost+2;
					qe.push(tmp);
				}
				else
				{
					vis[tx][ty]=1;
					tmp.x=tx;
					tmp.y=ty;
					tmp.cost=cur.cost+1;
					qe.push(tmp);
				}
			}
		}
	}
}
int main()
{ 
  while(~scanf("%d%d",&n,&m))
  {
  int xa,ya,cnt=0;
  memset(vis,0,sizeof(vis));
  ans=50000;
  for(int i=1;i<=n;i++)
  {
  	for(int j=1;j<=m;j++)
  	{
	  	scanf(" %c",&mapp[i][j]);
	  	if(mapp[i][j]=='a')
	  	{
	  		xa=i;
	  		ya=j;
	  		vis[i][j]=1;
	  	}
	  	else if(mapp[i][j]=='r')
	  	{
	  		cnt++;
	  	}
	  	else if(mapp[i][j]=='#')
	  	   vis[i][j]=1;
    }
  } 
  if(cnt==0)
    printf("Poor ANGEL has to stay in the prison all his life.n");
  else
  {
  	bfs(xa,ya);
  	if(ans==50000)
  	  printf("Poor ANGEL has to stay in the prison all his life.n");
    else
      printf("%dn",ans);
  }
  }
  return 0;	
}