Abandoned warehouse

#include <bits/stdc++.h>

int main() {
    std::ios_base::sync_with_stdio(false);
    std::cin.tie(nullptr);

    long long n, m;
    std::cin >> n >> m;

    int start = 0;
    int end = 0;
    std::vector<char> map(n*m);
    for (int i = 0; i < n; i++) {
        std::string line;
        std::cin >> line;
        for (int j = 0; j < m; j++) {
            map[i * m + j] = line[j];
            if (line[j] == 'A') start = i * m + j;
            if (line[j] == 'B') end = i * m + j;
        }
    }

    std::vector visited(n*m, false);
    std::vector parent(n*m, 0);
    std::vector move(n*m, ' ');

    visited[start]=true;
    std::queue<int> queue;
    queue.push(start);

    while (!queue.empty()) {
        const int v = queue.front();
        queue.pop();
        std::vector<int> ways;
        if (v >= m && map[v - m] != '#' && !visited[v - m]) {
            ways.push_back(v - m);
            move[v - m] = 'U';
        }
        if (v % m != 0 && map[v - 1] != '#' && !visited[v - 1]) {
            ways.push_back(v - 1);
            move[v - 1] = 'L';
        }
        if (v % m != m - 1 && map[v + 1] != '#' && !visited[v + 1]) {
            ways.push_back(v + 1);
            move[v + 1] = 'R';
        }
        if (v < (n-1)*m && map[v + m] != '#' && !visited[v + m]) {
            ways.push_back(v + m);
            move[v + m] = 'D';
        }

        for (int w : ways) {
            visited[w] = true;
            parent[w] = v;

            if (w == end) {
                std::string road;
                int pos = end;
                while (pos != start) {
                    road += move[pos];
                    pos = parent[pos];
                }
                std::ranges::reverse(road);
                std::cout << "YES\n" << road.size() << '\n' << road << std::endl;
                return 0;
            }
            queue.push(w);
        }
    }
    std::cout << "NO" << std::endl;
    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