1 #include<iostream>
  2 #include<sstream>
  3 #include<cstdio>
  4 #include<cstdlib>
  5 #include<string>
  6 #include<cstring>
  7 #include<algorithm>
  8 #include<functional>
  9 #include<iomanip>
 10 #include<numeric>
 11 #include<cmath>
 12 #include<queue>
 13 #include<vector>
 14 #include<set>
 15 #include<cctype>
 16 #define PI acos(-1.0)
 17 const int INF = 0x3f3f3f3f;
 18 const int NINF = -INF - 1;
 19 typedef long long ll;
 20 using namespace std;
 21 int n, m, flag;
 22 char maze[1005][1005];//迷宫
 23 typedef pair<int, int> P;
 24 int usedf[1005][1005], usedj[1005][1005];//火; 人 是否经过
 25 int d[1005][1005], tim[1005][1005];//人；火 时间
 26 int st, ed;//起点
 27 int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};
 28 queue<P> fire;
 29 void ini()//预处理大火覆盖所需时间（BFS）
 30 {
 31     while (fire.size())
 32     {
 33         P rec = fire.front();
 34         fire.pop();
 35         for (int i = 0; i < 4; ++i)
 36         {
 37             int nx = rec.first + dx[i], ny = rec.second + dy[i];
 38             if (nx >= 0 && nx < n && ny >= 0 && ny < m && !usedf[nx][ny] && maze[nx][ny] != '#')
 39             {
 40                 usedf[nx][ny] = 1;
 41                 fire.push(P(nx, ny));
 42                 tim[nx][ny] = tim[rec.first][rec.second] + 1;
 43             }
 44         }
 45     }
 46 }
 47 int bfs()
 48 {
 49     queue<P> q;
 50     memset(usedj, 0, sizeof(usedj));
 51     for (int i = 0; i < n; ++i)
 52     {
 53         for (int j = 0; j < m; ++j)
 54             d[i][j] = INF;
 55     }
 56     q.push(P(st, ed));
 57     usedj[st][ed] = 1;
 58     d[st][ed] = 0;
 59     P temp;
 60     while(q.size())
 61     {
 62         temp = q.front();
 63         q.pop();
 64         if (temp.first == 0 || temp.first == n - 1 || temp.second == 0 || temp.second == m - 1)//到达边界即逃出
 65         {
 66             flag = 1;
 67             break;
 68         }
 69         for (int i = 0; i < 4; ++i)
 70         {
 71             int nx = temp.first + dx[i], ny = temp.second + dy[i];
 72             if (nx >= 0 && nx < n && ny >= 0 && ny < m && !usedj[nx][ny] && maze[nx][ny] == '.' && d[temp.first][temp.second] + 1 < tim[nx][ny])
 73             {
 74                 usedj[nx][ny] = 1;
 75                 q.push(P(nx, ny));
 76                 d[nx][ny] = d[temp.first][temp.second] + 1;
 77             }
 78         }
 79     }
 80     if (flag) return d[temp.first][temp.second] + 1;
 81     else return -1;
 82 }
 83 int main()
 84 {
 85     int T;
 86     cin >> T;
 87     while (T--)
 88     {
 89         flag = 0;
 90         cin >> n >> m;
 91         memset(usedf, 0, sizeof(usedf));//预处理的BFS函数的初始化，写在这里方便输入时给特殊位置赋值
 92         for (int i = 0; i < n; ++i)
 93         {
 94             for (int j = 0; j < m; ++j)
 95                 tim[i][j] = INF;
 96         }
 97         for (int i = 0; i < n; ++i)
 98         {
 99             for (int j = 0; j < m; ++j)
100             {
101                 cin >> maze[i][j];
102                 if (maze[i][j] == 'J')  st = i, ed = j;
103                 if (maze[i][j] == 'F')
104                 {
105                     usedf[i][j] = 1;
106                     tim[i][j] = 0;
107                     fire.push(P(i, j));
108                 }
109             }
110         }
111         ini();
112         int ans = bfs();
113         if (ans != -1) cout << ans << endl;
114         else cout << "IMPOSSIBLE" << endl;
115         while(fire.size()) fire.pop();
116     }
117     return 0;
118 }