Abandoned warehouse

import sys
from collections import deque

data = sys.stdin.buffer.read().split()
n = int(data[0]); m = int(data[1])

W = m + 2
bar = b"#" * W
map = bar + b"".join(b"#" + data[2 + i] + b"#" for i in range(n)) + bar

start = map.find(b"A")
endd = map.find(b"B")

if start < 0 or endd < 0:
    print("NO")
    exit()

prev = [-1] * len(map)
mv = bytearray(len(map))
prev[start] = start
openSet = deque([start])

while openSet:
    cur = openSet.popleft()

    if cur == endd:
        out = bytearray()
        while cur != start:
            out.append(mv[cur])
            cur = prev[cur]
        out.reverse()
        sys.stdout.write("YES\n%d\n%s\n" % (len(out), out.decode()))
        break

    nx = cur + 1
    if prev[nx] < 0 and map[nx] != 35:
        prev[nx] = cur; mv[nx] = 82; openSet.append(nx)
    nx = cur - 1
    if prev[nx] < 0 and map[nx] != 35:
        prev[nx] = cur; mv[nx] = 76; openSet.append(nx)
    nx = cur - W
    if prev[nx] < 0 and map[nx] != 35:
        prev[nx] = cur; mv[nx] = 85; openSet.append(nx)
    nx = cur + W
    if prev[nx] < 0 and map[nx] != 35:
        prev[nx] = cur; mv[nx] = 68; openSet.append(nx)
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: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED