Shared code

#include <bits/stdc++.h>
using namespace std;
#define endl ("\n")
#define pi (3.141592653589)
#define mod 1000000007
#define int long long
#define pb push_back
#define mp make_pair
#define ff first
#define ss second
#define rep(i,n) for(int i=0;i<n;i++)
#define fast ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);




bool valid(int row, int cols, int n, int m){
    return (row >= 0 && row < n && cols >= 0 && cols < m);
}


int32_t main(){
    fast    
//   freopen("input.txt","r",stdin);
//	freopen("output.txt","w",stdout);
    int t=1;
//    cin>>t;
    while(t--){
    	int n, m;cin>>n>>m;
    int row[4] = {1, -1, 0, 0};
	int col[4] = {0, 0, 1, -1};
	
    vector<vector<char>>v(n, vector<char>(m));
    
    int vis[n][m];rep(i, n)rep(j, m)vis[i][j]=0;
    
    pair<int, int>start;
    
    rep(i, n){
    	rep(j, m){
    		cin>>v[i][j];
    		if(v[i][j]=='A')start=mp(i, j);
		}
	}

    list<pair<int, int>> q;
    
    vis[start.ff][start.ss]=1;
    q.pb(start);
    
    map<pair<int, int>, pair<pair<int, int>,char>>parent;
    
    while (!q.empty())
    {
        auto s=q.front();
        int a=s.ff, b=s.ss;
        q.pop_front();

        for(auto i :row){
            for(auto j :col){
                if(valid(a+i, b+j, n, m) and (abs(i) != abs(j)) and !vis[a+i][b+j] and (v[a+i][b+j] == '.' or v[a+i][b+j] == 'B') ){
                    char c;
                    if(i==1 and j==0)
                        c= 'D';
                    if(i==-1 and j==0)
                        c='U';
                    if(j==1 and i==0)
                        c='R';
                    if(j==-1 and i==0)
                        c='L';

                    parent[mp(a+i, b+j)]=mp(mp(a, b),c);

                    if(v[a+i][b+j] == 'B'){
                        auto end = make_pair(a+i, b+j);
                        string res = "";
                        while(true){
                            res += parent[end].ss;
                            end = parent[end].ff;
                            if(end.ff == start.ff and end.ss == start.ss){
                                break;
                            }
                        }
                        reverse(res.begin(), res.end()); 
                        cout<<"YES"<<endl;
                        cout<<res.length()<<endl;
                        cout<<res;
                        return 0;
                    }

                    vis[a+i][b+j]=1;
                    q.pb(mp(a+i, b+j));
                }
            }
        }
    }
    cout<<"NO";
    }
    return 0;
}