Abandoned warehouse

import sys
from collections import deque

input = sys.stdin.readline
n, m = map(int, input().split())

warehouse = [input().rstrip('\n') for _ in range(n)]
start = None
end = None
for i in range(n):
    row = warehouse[i]
    a = row.find('A')
    if a != -1:
        start = (i, a)
    b = row.find('B')
    if b != -1:
        end = (i, b)
if start is None or end is None:
    print("NO")
    sys.exit()

start_id = start[0] * m + start[1]
end_id = end[0] * m + end[1]

visited = bytearray(n * m)
prev_node = [-1] * (n * m)
prev_dir = [''] * (n * m)
moves = ((-1, 0, 'U'), (1, 0, 'D'), (0, -1, 'L'), (0, 1, 'R'))

visited[start_id] = 1
queue = deque([start])
found = False

while queue:
    row, col = queue.popleft()
    if row * m + col == end_id:
        found = True
        break
    for dr, dc, direction in moves:
        next_row, next_col = row + dr, col + dc
        if 0 <= next_row < n and 0 <= next_col < m:
            nid = next_row * m + next_col
            if not visited[nid] and warehouse[next_row][next_col] != '#':
                visited[nid] = 1
                prev_node[nid] = row * m + col
                prev_dir[nid] = direction
                queue.append((next_row, next_col))

if not visited[end_id]:
    print("NO")
else:
    path = []
    current = end_id
    while current != start_id:
        path.append(prev_dir[current])
        current = prev_node[current]
    path.reverse()
    print("YES")
    print(len(path))
    print(''.join(path))

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