Escape! If you want to survive [NCTU Floor 13]

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int row, col;

bool validPosition(int n, int m){
    if(n < 0 || n == row || m < 0 || m == col)
        return false;
    return true;
}

void fireSpread(vector <string> &map){
    vector <string> modified = map;
    for(int i = 0; i < row; i++){
        for(int j = 0; j < col; j++){
            if(map[i][j] == 'F'){
                if(validPosition(i - 1, j))
                    modified[i - 1][j] = 'F';
                if(validPosition(i + 1, j))
                    modified[i + 1][j] = 'F';
                if(validPosition(i, j - 1))
                    modified[i][j - 1] = 'F';
                if(validPosition(i, j + 1))
                    modified[i][j + 1] = 'F';
            }
        }
    }
    map = modified;
}

int findMinimum(vector <string> map, int n, int m, vector <vector<int>> dp, vector <vector<bool>> visited){
    if(n == 0 || m == 0 || n == (row - 1) || m == (col - 1))
        return 0;
    if(dp[n][m] != -1)
        return dp[n][m];
    visited[n][m] = true;

    int up, down, left, right;
    up = down = left = right = 1e6;

    fireSpread(map);
    if(map[n - 1][m] == '.'){
        if(!visited[n - 1][m]){
            up = 1 + findMinimum(map, n - 1, m, dp, visited);
            //cout << "Up!" << endl;
        }
    }
    if(map[n + 1][m] == '.'){
        if(!visited[n + 1][m]){
            down = 1 + findMinimum(map, n + 1, m, dp, visited);
            //cout << "Down!" << endl;
        }
    }
    if(map[n][m - 1] == '.'){
        if(!visited[n][m - 1]){
            left = 1 + findMinimum(map, n, m - 1, dp, visited);
            //cout << "Left!" << endl;
        }
    }
    if(map[n][m + 1] == '.'){
        if(!visited[n][m + 1]){
            right = 1 + findMinimum(map, n, m + 1, dp, visited);
            //cout << "Right!" << endl;
        }

    }

    dp[n][m] = min(up, min(down, min(left, right)));
    return dp[n][m];
}

int solve(vector <string> map){
    int x = -1, y = -1;
    for(int i = 0; i < row && x == -1; i++){
        for(int j = 0; j < col; j++){
            if(map[i][j] == 'J'){
                x = i;
                y = j;
                break;
            }
        }
    }
    vector <vector<int> > dp(row, vector<int>(col, -1));
    vector <vector<bool> > visited(row, vector<bool>(col, false));

    int res = findMinimum(map, x, y, dp, visited);

    return (res >= 1e6 ? -1 : res);
}

int main(){
    cin >> row >> col;
    string str;
    vector <string> map;
    for(int i = 0; i < row; i++){
        cin >> str;
        map.push_back(str);
    }
    int res = 1 + solve(map);
    if(res - 1 == -1)
        cout << "N" << endl;
    else
        cout << res << endl;
    return 0;
}