Abandoned warehouse

#ifdef ONPC
    #define _GLIBCXX_DEBUG
#endif
#include <bits/stdc++.h>

#define char unsigned char
#define rep(i, a, b) for(int i=a; i< (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
#define eb emplace_back
#define mp make_pair
#define mt make_tuple
#define fi first
#define se second
#define pb push_back

#define LSOne(S) ((S) & -(S))

using namespace std;
// mt19937 rnd(239);
mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());

typedef long long C;
typedef complex<C> P;
#define X real()
#define Y imag()

template<class T>
istream& operator>> (istream& is, complex<T>& p) {
    T value;
    is >> value;
    p.real(value);
    is >> value;
    p.imag(value);
    return is;
}

typedef long long ll;
typedef long double ld;

using pi = pair<ll, ll>;
using vi = vector<ll>;
template <class T>
using pq = priority_queue<T>;
template <class T>
using pqg = priority_queue<T, vector<T>, greater<T>>;

int popcnt(int x) { return __builtin_popcount(x); }
int popcnt(ll x) { return __builtin_popcountll(x); }

#define MIN(v) *min_element(all(v))
#define MAX(v) *max_element(all(v))
#define LB(c, x) distance((c).begin(), lower_bound(all(c), (x)))
#define UB(c, x) distance((c).begin(), upper_bound(all(c), (x)))

void __print(int x) {cerr << x;}
void __print(long x) {cerr << x;}
void __print(long long x) {cerr << x;}
void __print(unsigned x) {cerr << x;}
void __print(unsigned long x) {cerr << x;}
void __print(unsigned long long x) {cerr << x;}
void __print(float x) {cerr << x;}
void __print(double x) {cerr << x;}
void __print(long double x) {cerr << x;}
void __print(char x) {cerr << '\'' << x << '\'';}
void __print(const char *x) {cerr << '\"' << x << '\"';}
void __print(const string &x) {cerr << '\"' << x << '\"';}
void __print(bool x) {cerr << (x ? "true" : "false");}

template<typename T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ", "; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? ", " : ""), __print(i); cerr << "}";}
void _print() {cerr << "]\n";}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
#ifdef DEBUG
#define dbg(x...) cerr << "\e[91m"<<__func__<<":"<<__LINE__<<" [" << #x << "] = ["; _print(x); cerr << "\e[39m" << endl;
#else
#define dbg(x...)
#endif

template<typename S, typename T = S> void chmin(S &s, T t) {s = s < t ? s : t;}
template<typename S, typename T = S> void chmax(S &s, T t) {s = s > t ? s : t;}

const int INF = 1e9; // 10^9 = 1B is < 2^31-1
const ll LLINF = 4e18; // 4*10^18 is < 2^63-1
const double EPS = 1e-9;
const ll MOD = 1e9+7;

const int N=1010;
int v[N][N];
bool vis[N][N];

int dp[N][N];
int n,m;

int dx[4]={0, 1, 0, -1}, dy[4]={1, 0, -1, 0};

bool ok(int i, int j) {
    return i>=0 && j>=0 && i<n && j<m && v[i][j];
}

int solve() {
    std::cin >> n >> m;

    pair<int, int> s={-1, -1}, t={-1, -1};

    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            dp[i][j]=-1;
            vis[i][j]=false;
        }
    }

    
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            char c; std::cin >> c;
            v[i][j]=(c=='#' ? 0 : 1);
            if(c=='A') s={i, j};
            if(c=='B') t={i, j};
        }
    }

    dp[s.fi][s.se]=-2;

    queue<pair<int,int>> q;
    q.push(s);

    while(!q.empty()) {
        pair<int,int> curr=q.front();
        int x=curr.fi, y=curr.se;
        q.pop();
        if(vis[x][y]) continue;
        vis[x][y]=true;
        for (int i = 0; i < 4; i++) {
            int newX=x+dx[i], newY=y+dy[i];
            if(ok(newX, newY) && !vis[newX][newY]) {
                q.push({newX, newY});
                dp[newX][newY]=i;
            }
        }
    }

    if(false)
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            if(dp[i][j]==0) {
                std::cout << "L";
            } else if(dp[i][j]==1) {
                std::cout << "U";
            } else if(dp[i][j]==2) {
                std::cout << "R";
            } else if(dp[i][j]==3) {
                std::cout << "D";
            } else std::cout << "-";
        }
        //std::cout  << std::endl;
    }
    dp[s.fi][s.se]=-2;


    if(dp[t.fi][t.se]==-1) {
        std::cout << "NO" << std::endl;
        return 0;
    }

    std::cout << "YES" << std::endl;
    int curr=dp[t.fi][t.se];
    int x=t.fi, y=t.se;

    string res="";

    while(curr!=-2) {
        //std::cout << x << "  " << y << std::endl;
        if(dp[x][y]==0) {
            res+="R";
            y--;
        } else if(dp[x][y]==1) {
            res+="D";
            x--;
        } else if(dp[x][y]==2) {
            res+="L";
            y++;
        } else {
            res+="U";
            x++;
        }
        curr=dp[x][y];
    }

    reverse(all(res));
    std::cout << res.size() << std::endl;
    std::cout << res << std::endl;



    return 0;
}

int32_t main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    int TET = 1;
    //cin >> TET;
    for (int i = 1; i <= TET; i++) {
        #ifdef ONPC
            cout << "TEST CASE#" << i << endl;
        #endif
        
        if (solve()) {
            break;
        }

        #ifdef ONPC
            cout << "__________________________" << endl;
        #endif
    }
    #ifdef ONPC
        cerr << endl << "finished in " << clock() * 1.0 / CLOCKS_PER_SEC << " sec" << endl;
    #endif
}

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