与其说是训练不如说是重温。重新写了Java版本的代码。

import java.util.*;import java.math.*;import java.io.BufferedInputStream;public class Main{    static class Node    {    int r, c, t;    public Node(int _r, int _c)    {        this(_r, _c, 0);    }    public Node(int _r, int _c, int _t)    {        r=_r; c=_c; t=_t;    }    }    static int[][] fireTime = new int[1005][1005];    static int[][] maze = new int[1005][1005];    static Queue
    
      q = new LinkedList<>();    static final int[] dx = {0,1,0,-1};    static final int[] dy = {1,0,-1,0};    static int r, c;    static int startR, startC;    static void getFireTime()    {    for(int i=0;i<=r;++i)        for(int j=0;j<=c;++j)        fireTime[i][j]=0x3f3f3f3f;    while(!q.isEmpty())    {        Node node = q.poll();        fireTime[node.r][node.c] = node.t;        for(int i=0; i!=4; ++i)        {        int tr = node.r + dx[i],            tc = node.c + dy[i];        if(tr>=0 && tr
     
      =0 && tc
      
       node.t+1 && maze[tr][tc]==1)        {            fireTime[tr][tc] = node.t+1;            q.offer(new Node(tr, tc, node.t+1));        }        }    }    }    static String solve()    {    Queue
       
         sq = new LinkedList<>();    boolean[][] vis = new boolean[1005][1005];    sq.offer(new Node(startR, startC));    vis[startR][startC]=true;    while(!sq.isEmpty())    {        Node now = sq.poll();        if(now.t>=fireTime[now.r][now.c]) continue;        if(now.r==0 || now.r == r-1 || now.c == 0 || now.c == c-1)        return String.valueOf(now.t+1);        for(int i=0;i!=4;++i)        {        int tr = now.r + dx[i],            tc = now.c + dy[i];        if(tr>=0 && tr
        
         =0 && tc
         
          now.t+1 && (!vis[tr][tc]) && maze[tr][tc]==1) { vis[tr][tc]=true; sq.offer(new Node(tr, tc, now.t+1)); } } } return "IMPOSSIBLE"; } public static void main(String args[]) { Scanner cin = new Scanner(new BufferedInputStream(System.in)); int T = cin.nextInt(); while(T-- != 0) { q.clear(); r = cin.nextInt(); c = cin.nextInt(); for(int i=0; i!=r; ++i) { String str = cin.next(); for(int j=0;j!=c;++j) { char chr = str.charAt(j); if(chr == '#') maze[i][j] = 0; else if(chr == '.') maze[i][j] = 1; else if(chr == 'J') { maze[i][j] = 1; startR=i; startC=j; } else if(chr == 'F') { maze[i][j] = 1; q.offer(new Node(i,j)); } } } getFireTime(); System.out.println(solve()); } }}