Shared code

#include <bits/stdc++.h>
using namespace std;
#define FIO                       \
    ios_base::sync_with_stdio(0); \
    cin.tie(0);                   \
    cout.tie(0)
#define mod 1000000007
#define ff first
#define ss second
#define int long long
#define pb push_back
#define mp make_pair
#define mt make_tuple
#define pii pair<int, int>
#define vi vector<int>
#define mii map<int, int>
#define endl "\n"
/* --------------------------------------------------------------------------------------------------*/
#define ms(arr, v) memset(arr, v, sizeof(arr))
#define asc(i, a, n) for (int i = a; i < n; i++)
#define dsc(i, a, n) for (int i = n - 1; i >= a; i--)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
/*----------------------------------------------------------------------------------------------------*/

vector< vector<int> > dir = {{0, 1}, {1, 0}, { -1, 0}, {0, -1}};
vector<char> moves = {'R', 'D', 'U', 'L'};
void solve()
{
	int n, m;
	cin >> n >> m;
	char a[n][m];
	int sx, sy, ex, ey;

	asc(i, 0, n)
	{
		asc(j, 0, m)
		{
			cin >> a[i][j];
			if (a[i][j] == 'A')
			{
				sx = i;
				sy = j;
				a[i][j] = '.';

			}

			if (a[i][j] == 'B')
			{
				ex = i;
				ey = j;
				a[i][j] = '.';

			}

		}
	}
	string res = "";
	queue<pair<int, int>> q;
	q.push({sx, sy});
	vector< vector< pair<char, pair<int, int> > > > ds(n, vector< pair<char, pair<int, int> > >( m, { 'N', { -1, -1} } ) );
	while (!q.empty())
	{
		auto curr = q.front();
		q.pop();
		a[curr.first][curr.second] = '#';
		if (curr.first == ex && curr.second == ey)
			break;
		for (int i = 0; i < 4; i++)
		{
			int x = curr.first + dir[i][0];
			int y = curr.second + dir[i][1];

			if (x < 0 || y < 0 || x >= n || y >= m || a[x][y] == '#')
			{
				continue;
			}
			q.push({x, y});
			ds[x][y] = { moves[i], {curr.first, curr.second} }  ;
		}

	}

	if (a[ex][ey] == '.')
	{
		cout << "NO" << endl;
		return;
	}
	cout << "YES" << endl;
	// cout << sx << " " << sy << endl;
	while (ex != sx || ey != sy)
	{
		res += ds[ex][ey].first;
		auto t = ds[ex][ey].second;
		ex = t.first;
		ey = t.second;
	}
	reverse(res.begin(), res.end());
	cout << res.size() << endl;
	cout << res << endl;
}


int32_t main()
{
	FIO;
// #ifndef ONLINE_JUDGE
// 	freopen("input.txt", "r", stdin);
// 	freopen("output.txt", "w", stdout);
// #endif

	// int t;
	// cin >> t;
	// while (t--)
	solve();
	return 0;
}