Abandoned warehouse

import sys
from collections import deque


def iix(i: int, j: int) -> int:
    return i * m + j


input = sys.stdin.readline

n, m = map(int, input().split())
inpt = []
for _ in range(n):
    inpt.append(list(input()))


start_node = (0, 0)
exit_node = (0, 0)
got1 = False
got2 = False
for i in range(n):
    for j in range(m):
        if inpt[i][j] == "A":
            start_node = (i, j)
            got1 = True
        elif inpt[i][j] == "B":
            exit_node = (i, j)
            got2 = True
        if got1 and got2:
            break


moves = [
    (1, 0),
    (-1, 0),
    (0, 1),
    (0, -1),
]

q = deque([start_node])
prev = [-1] * (n * m)


def bfs() -> bool:
    while q:
        i, j = q.popleft()
        if (i, j) == exit_node:
            return True
        for ii, jj in moves:
            if 0 <= i + ii < n and 0 <= j + jj < m and inpt[i + ii][j + jj] != "#":
                ix = iix(i + ii, j + jj)
                if prev[ix] == -1:
                    prev[ix] = iix(i, j)
                    q.append((i + ii, j + jj))

    return False


found = bfs()

if found:
    print("YES")
    node = iix(exit_node[0], exit_node[1])
    sn = iix(start_node[0], start_node[1])
    trace = [node]
    while node != sn:
        node = prev[node]
        trace.append(node)
    print(len(trace) - 1)

    node = trace.pop()
    out = ""
    while len(trace) > 0:
        next = trace[-1]
        if next > node:
            if next == node + 1:
                out += "R"
            else:
                out += "D"
        else:
            if next == node - 1:
                out += "L"
            else:
                out += "U"
        node = trace.pop()
    print(out)
else:
    print("NO")

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: TIME LIMIT EXCEEDED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED