Abandoned warehouse

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

int df[] = {-1, 1, 0, 0};
int dc[] = {0, 0, -1, 1};
char dir_char[] = {'U', 'D', 'L', 'R'};
 
struct Step {
    int prev_i, prev_j;
    char move;
};
 
int main() {
    int n, m;
    if (!(cin >> n >> m)) return 0;
 
    vector<vector<char>> map(n, vector<char>(m));
    int ini = -1, inj = -1;
    int end_i = -1, end_j = -1;
 
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            cin >> map[i][j];
            if (map[i][j] == 'A') {
                ini = i;
                inj = j;
            } else if (map[i][j] == 'B') {
                end_i = i;
                end_j = j;
            }
        }
    }
 
    vector<vector<Step>> parent(n, vector<Step>(m, {-1, -1, ' '}));
    vector<vector<bool>> visited(n, vector<bool>(m, false));
 
    queue<pair<int, int>> q;
    q.push({ini, inj});
    visited[ini][inj] = true;
    bool found = false;
 
    while (!q.empty()) {
        auto [i, j] = q.front();
        q.pop();
 
        if (i == end_i && j == end_j) {
            found = true;
            break;
        }
 
        for (int k = 0; k < 4; k++) {
            int ni = i + df[k];
            int nj = j + dc[k];
 
            if (ni >= 0 && ni < n && nj >= 0 && nj < m) {
                if (!visited[ni][nj] && map[ni][nj] != '#') {
                    visited[ni][nj] = true;
                    parent[ni][nj] = {i, j, dir_char[k]};
                    q.push({ni, nj});
                }
            }
        }
    }
 
    if (!found) {
        cout << "NO\n";
    } else {
        cout << "YES\n";
        
        vector<char> bestpath;
        int curr_i = end_i;
        int curr_j = end_j;
 
        while (curr_i != ini || curr_j != inj) {
            Step p = parent[curr_i][curr_j];
            bestpath.push_back(p.move);
            curr_i = p.prev_i;
            curr_j = p.prev_j;
        }
 
        reverse(bestpath.begin(), bestpath.end());
 
        cout << bestpath.size() << "\n";
        for (char c : bestpath) {
            cout << c;
        }
        cout << "\n";
    }
 
    return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED