究极坐牢，刚开始思路没错但是TLE了，直接套了两层bfs也难怪
以为自己终于可以自己写出来一次，还是去看别人代码调了，直接两次bfs，刚开始想到了，但是感觉不如模拟来的直观（火先走，人再走）

淦，图书馆坐了四个小时，一上午两道题，颈椎很难顶，下午去健身房了…

#include <iostream>
#include <queue>
#include <cstring>

#define x first
#define y second 

using namespace std;
typedef pair<int, int> PII;

const int N = 1010;

int t;
int n, m;
char g[N][N];
int dj[N][N], df[N][N];
PII pf, pj;
int dx[] = {-1, 0, 1, 0}, dy[] = {0, -1, 0, 1};

void bfs1() {
    queue<PII> qf;

    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            if (g[i][j] == 'F') {
                pf.x = i, pf.y = j;
                df[i][j] = 0;
                qf.push(pf);
            }
        }
    }


    while (qf.size()) {


        PII tf = qf.front();
        qf.pop();

        for (int i = 0; i < 4; i++) {
            int a = tf.x + dx[i], b = tf.y + dy[i];
            if (a < 0 || a > n - 1 || b < 0 || b > m - 1 || g[a][b] == '#' || df[a][b] != -1)
                continue;
            df[a][b] = df[tf.x][tf.y] + 1;

            pf.x = a, pf.y = b;
            qf.push(pf);
        }
    }
}

void bfs2(PII J) {
    queue<PII> q;
    q.push(J);

    dj[J.x][J.y] = 0;

    while (q.size()) {

        PII t = q.front();
        q.pop();

        if (t.x == 0 || t.y == 0 || t.x == n - 1 || t.y == m - 1) {
            printf("%d\n", dj[t.x][t.y] + 1); // 从出口出去还要加1
            return;
        }


        for (int i = 0; i < 4; i++) {

            int a = t.x + dx[i], b = t.y + dy[i];
            if (g[a][b] == '#' || dj[a][b] != -1 || (df[a][b] != -1 && dj[t.x][t.y] + 1 >= df[a][b])) 
                continue;
            dj[a][b] = dj[t.x][t.y] + 1;
            pj.x = a, pj.y = b;
            q.push(pj);
        }
    }

    printf("IMPOSSIBLE\n");
}

int main() {
    cin >> t;
    while (t--) {
        cin >> n >> m;
        PII J, F;
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                cin >> g[i][j];
                if (g[i][j] == 'J')
                    J.x = i, J.y = j;
            }
        }

        memset(dj, -1, sizeof dj);
        memset(df, -1, sizeof df);

        bfs1();
        bfs2(J);
    }
    return 0;
}