Abandoned warehouse

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


int main() {
  int n, m;
  cin >> n >> m;
  vector<string> g(n);
  for (string &row : g) cin >> row;

  int start = -1, goal = -1;
  for (int i = 0; i < n; i++)
    for (int j = 0; j < m; j++) {
      if (g[i][j] == 'A') start = i * m + j;
      if (g[i][j] == 'B') goal = i * m + j;
    }

  const int di[4] = {-1, 1, 0, 0}, dj[4] = {0, 0, -1, 1};
  const char mv[4] = {'U', 'D', 'L', 'R'};

  vector<char> came(n * m, 0);
  came[start] = 'S';
  vector<int> q{start};
  for (size_t head = 0; head < q.size(); head++) {
    int cur = q[head];
    int i = cur / m, j = cur % m;
    for (int d = 0; d < 4; d++) {
      int ni = i + di[d], nj = j + dj[d], move = ni * m + nj;
      if (ni < 0 || ni >= n || nj < 0 || nj >= m || g[ni][nj] == '#' || came[move]) continue;
      came[move] = mv[d];
      q.push_back(move);
    }
  }

  if (!came[goal]) {
    cout << "NO\n";
    return 0;
  }

  string path;
  for (int cur = goal; cur != start;) {
    char c = came[cur];
    path += c;
    int d = c == 'U' ? 0 : c == 'D' ? 1 : c == 'L' ? 2 : 3;
    cur -= di[d] * m + dj[d];
  }
  reverse(path.begin(), path.end());

  cout << "YES\n" << path.size() << "\n" << path << "\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