path printing

#include "bits/stdc++.h"

using namespace std;

int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};
char dir[4] = {'D', 'R', 'U', 'L'};

const int maxN = 1010;

char grid[maxN][maxN];
bool visited[maxN][maxN];
pair<int,int> parent[maxN][maxN];

void bfs (int x, int y, int n, int m) {
	queue<pair<int,int>> q;
	q.push(make_pair(x, y));
	parent[x][y] = {-1, -1};
	visited[x][y] = true;
	while (!q.empty()) {
		pair<int,int> u = q.front();
		q.pop();
		for (int i = 0; i < 4; ++i) {
			int dxx = u.first + dx[i];
			int dyy = u.second + dy[i];
			if (dxx >= 1 and dxx <= n and dyy >= 1 and dyy <= m and !visited[dxx][dyy] and grid[dxx][dyy] != '#') {
				visited[dxx][dyy] = true;
				q.push(make_pair(dxx, dyy));
				parent[dxx][dyy] = u;
			}
		}
	}
}

int main () {
	 ios::sync_with_stdio(false);
	 cin.tie(nullptr);
	 cout.tie(nullptr);
	 int n, m;
	 cin >> n >> m;
	 int start_x, start_y, end_x, end_y;
	 for (int i = 1; i <= n; ++i) {
		 for (int j = 1; j <= m; ++j) {
			 cin >> grid[i][j];
			 if (grid[i][j] == 'A') {
				 start_x = i, start_y = j;
			 }
			 if (grid[i][j] == 'B') {
				 end_x = i, end_y = j;
			 }
		 }
	 }
	 bfs(start_x, start_y, n, m);
	 if (!visited[end_x][end_y]) {
		 cout << "NO\n";
	 } else {
		 cout << "YES\n";
		 vector<pair<int, int>> path;
		 path.push_back(make_pair(end_x, end_y));
		 int x = end_x, y = end_y;
		 while (parent[x][y] != make_pair(-1, -1)) {
			 pair<int,int> p = parent[x][y];
			 x = p.first, y = p.second;
			 path.push_back(make_pair(x, y));
		 }
		 reverse(path.begin(), path.end());
		 //~ for (pair<int,int> p : path) {
			 //~ cout << '{' << p.first << ',' << p.second << "} => ";
		 //~ }
		 string res = "";
		 for (int i = 0; i < (int) path.size() - 1; ++i) {
			 for (int j = 0; j < 4; ++j) {
				 int dxx = path[i].first + dx[j];
				 int dyy = path[i].second + dy[j];
				 if (dxx == path[i + 1].first and dyy == path[i + 1].second) {
					 res.push_back(dir[j]);
					 break;
				 }
			 }
		 }
		 cout << (int) res.size() << '\n';
		 cout << res << '\n';
	 }
}