HDU 1242 rescue (BFS (breadth-first search ))

Rescue

Time Limit: 2000/1000 MS (Java/others) memory limit: 65536/32768 K (Java/Others)

Total submission (s): 12441 accepted submission (s): 4551 problem descriptionangel 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 Wils, 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 .)

Inputfirst 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.

Outputfor each test case, your program shocould output a single integer, standing for the minimal time needed. if such a number does no exist, you showould 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

Train of Thought: BFS (breadth-first search)

import java.io.*;import java.util.*;public class Main {Queue<Node> que=new LinkedList<Node>();int n,m,sx,sy;char ch[][];int fx[]={1,-1,0,0};int fy[]={0,0,1,-1};boolean boo[][]=new boolean[202][202];public static void main(String[] args) {new Main().work();}void work(){    Scanner sc=new Scanner(new BufferedInputStream(System.in));    while(sc.hasNext()){    que.clear();    n=sc.nextInt();    m=sc.nextInt();    ch=new char[n][m];    for(int i=0;i<n;i++){    String s=sc.next();    ch[i]=s.toCharArray();    Arrays.fill(boo[i],false);    }    Node bode=new Node();    for(int i=0;i<n;i++){    for(int j=0;j<m;j++){    if(ch[i][j]=='a'){    bode.x=i;    bode.y=j;    }    }    }    boo[bode.x][bode.y]=true;    bode.t=0;    que.add(bode);    BFS();    }    }void BFS(){    while(!que.isEmpty()){    Node bode=que.poll();    if(ch[bode.x][bode.y]=='r'){    System.out.println(bode.t);    return;    }    for(int i=0;i<4;i++){    int px=bode.x+fx[i];int py=bode.y+fy[i];    if(check(px,py)&&!boo[px][py]){    Node t1=new Node();    if(ch[px][py]=='x'){    t1.t=bode.t+2;    }    else{    t1.t=bode.t+1;    }    t1.x=px;    t1.y=py;    boo[px][py]=true;    que.add(t1);    }    }    }    System.out.println("Poor ANGEL has to stay in the prison all his life.");    }boolean check(int px,int py){if(px<0|px>n-1||py<0||py>m-1||ch[px][py]=='#')return false;return true;}class Node{int x;int y;int t; }}