Revise paste Untitled

#include <iostream>
#include <bits/stdc++.h>
#include <fstream>
#include <string>
#include <set>
#include <cstring>
#include <queue>
#define ll long long
#define ld long double
#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define eb emplace_back
#define all(x) (x).begin(), (x).end()
#define INF 1e18
#define eps 0.00001
#define le length
#define MOD 1000000007
using namespace std;
ll memo[2005][2005];
int prices[1005];
int pages[1005];
int n;
int x;

char mat[1005][1005];
int prev_steps[1005][1005];
int main() {
//    ifstream cin ("input.txt");
    int n, m;
    cin >> n >> m;
    int ei, ej, si, sj;
    int di[] = {-1, 1, 0, 0};
    int dj[] = {0, 0, -1, 1};
    for(int i = 0; i < n; i++) {
        for(int j =0 ; j < m; j++) {
            cin >> mat[i][j];
            if(mat[i][j] == 'A') {
                si = i;
                sj = j;
            }
            if(mat[i][j] == 'B') {
                ei = i;
                ej = j;
            }
        }
    }
    queue<int> q;
    q.push(si);
    q.push(sj);
    q.push(0);
    vector<vector<bool> > visited(n + 1, vector<bool>(m + 1, false));
    visited[si][sj] = true;
    int path = -1;
    while(!q.empty()) {
        int ci = q.front(); q.pop();
        int cj = q.front(); q.pop();
        int dist = q.front(); q.pop();
        if(ci == ei and cj == ej) {
            path = dist;
            break;
        }
        for(int i = 0; i < 4; i++) {
            int ti = ci + di[i];
            int tj = cj + dj[i];
            if(ti >= 0 and ti < n and tj >= 0 and tj < m and !visited[ti][tj] and mat[ti][tj] != '#') {
                q.push(ti);
                q.push(tj);
                q.push(dist + 1);
                prev_steps[ti][tj] = i;
                visited[ti][tj] = true;
            }
        }
    }
    
    if(path == -1) {
        cout << "NO";
        return 0;
    }
    cout << "YES\n" << path << endl;
    pair<int, int> S = {si, sj}, E = {ei, ej};
    string res = "";
    while(E != S) {
        int direction = prev_steps[E.first][E.second];
        
        if(direction == 0) {
            res += "U";
        }
        else if(direction == 1) {
            res += "D";
        }
        else if(direction == 2) {
            res += "L";
        }
        else {
            res += "R";
        }
        E = {E.first - di[direction], E.second - dj[direction]};
    }
    reverse(res.begin(), res.end());
    cout << res << endl;
    return 0;
}