Лабиринт (обход в ширину)

#include <iostream>
#include <cstdio>
#include <fstream>
#include <vector>
#include <algorithm>
#include <set>
#include <queue>
#include <cstring>

using namespace std;


const int INF = 100000;

int m, n;
int i, j;
vector<vector<char>> a;
vector<vector<int> > res;
bool check(int ii, int jj){  // проверка на границы
    if(ii < 0)
        return 0;
    if(ii >= m)
        return 0;
    if(jj < 0)
        return 0;
    if(jj >= n)
        return 0;
    if(a[ii][jj] == 'X')
        return 0;
    if(res[ii][jj] < res[i][j])
        return 0;
    return 1;
}
int main() {
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
    cin >> m >> n;
    a.resize(100, vector<char> (100));
    res.resize(100, vector<int> (100, 100000));
    int idxi = 101, idxj;
    queue<pair<int, int>> q;
    for(int i = 0; i < m; i++){
        for(int j = 0; j < n; ++j){
            cin >> a[i][j];
            if(a[i][j] == 'S'){
                q.push(make_pair(i, j));
                res[i][j] = 0;
            }
            if(a[i][j] == 'F'){
                idxi = i;
                idxj = j;
            }
        }
    }

    while(q.size()){  // обход в ширину
        auto t = q.front();
        i = t.first;
        j = t.second;
        if(check(i, j - 1)){
            res[i][j - 1] = res[i][j] + 1;
            q.push(make_pair(i, j - 1));
        }
        if(check(i, j + 1)){
            res[i][j + 1] = res[i][j] + 1;
            q.push(make_pair(i, j + 1));
        }
        if(check(i + 1, j)){
            res[i + 1][j] = res[i][j] + 1;
            q.push(make_pair(i + 1, j));
        }
        if(check(i - 1, j)){
            res[i - 1][j] = res[i][j] + 1;
            q.push(make_pair(i - 1, j));
        }
        q.pop();
    }
    if(res[idxi][idxj] == 100000){
        cout << -1;
    }
    else{
        cout << res[idxi][idxj];
    }

    return 0;
}