Labyrinth

#include <bits/stdc++.h>

using namespace std;

const int N = 1003;

int n, m;
int vis[N][N], d[N][N];
char c[N][N];

int main(){
    memset(d, -1, sizeof(d));
    cin >> n >> m;

    pair <int, int> Begin, End;

    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            cin >> c[i][j];
            if (c[i][j] == 'A') {
                Begin = make_pair(i, j);
            }
            if (c[i][j] == 'B') {
                End = make_pair(i, j);
            }
        }
    }

    queue < pair <int, int> > q;
    vis[Begin.first][Begin.second] = 1;
    d[Begin.first][Begin.second] = 0;
    q.push(Begin);

    while (!q.empty()) {
        pair <int, int> v = q.front();
        int x = v.first, y = v.second;
        q.pop();
        if ((c[x - 1][y] == '.' || c[x - 1][y] == 'B') && vis[x - 1][y] == 0) {
            vis[x - 1][y] = 1;
            d[x - 1][y] = d[x][y] + 1;
            q.push({x - 1, y});
        }
        if ((c[x + 1][y] == '.' || c[x + 1][y] == 'B') && vis[x + 1][y] == 0) {
            vis[x + 1][y] = 1;
            d[x + 1][y] = d[x][y] + 1;
            q.push({x + 1, y});
        }
        if ((c[x][y - 1] == '.' || c[x][y - 1] == 'B') && vis[x][y - 1] == 0) {
            vis[x][y - 1] = 1;
            d[x][y - 1] = d[x][y] + 1;
            q.push({x, y - 1});
        }
        if ((c[x][y + 1] == '.' || c[x][y + 1] == 'B') && vis[x][y + 1] == 0) {
            vis[x][y + 1] = 1;
            d[x][y + 1] = d[x][y] + 1;
            q.push({x, y + 1});
        }
    }

    if (vis[End.first][End.second] == 0) {
        cout << "NO\n";
        return 0;
    }

    cout << "YES\n";
    cout << d[End.first][End.second] << endl;

    string path;

    while (End != Begin) {
        if (d[End.first][End.second] - 1 == d[End.first - 1][End.second]) {
            End.first--;
            path += 'D';
            continue;
        }
        if (d[End.first][End.second] - 1 == d[End.first + 1][End.second]) {
            End.first++;
            path += 'U';
            continue;
        }
        if (d[End.first][End.second] - 1 == d[End.first][End.second - 1]) {
            End.second--;
            path += 'R';
            continue;
        }
        if (d[End.first][End.second] - 1 == d[End.first][End.second + 1]) {
            End.second++;
            path += 'L';
            continue;
        }
    }

    reverse(path.begin(), path.end());

    cout << path << endl;
}