Abandoned warehouse

from collections import deque

n, m = input().split()
n = int(n); m = int(m)

map = [[] for _ in range(n)]          # (1) m -> n
CHAR = {"#":1, ".":0, "A":0, "B":0}

start = None
endd = None
for i in range(n):
    s = input()
    map[i] = [CHAR[c] for c in s]
    idx = s.find("A")
    if idx != -1:
        start = (i, idx)
    idxB = s.find("B")
    if idxB != -1:
        endd = (i, idxB)

if start is None or endd is None:
    print("NO")
    exit()

si, js = start
ie, je = endd

visited = {start}
cameFrom = {}
openSet = deque([start])

while openSet:
    i, j = openSet.popleft()

    if i == ie and j == je:
        out = []
        cur = (i, j)
        while cur != start:
            cur, c = cameFrom[cur]
            out.append(c)
        out.reverse()
        s = "".join(out)
        print("YES")
        print(len(s))
        print(s)
        break

    for ni, nj, c in ((i, j+1, "R"), (i, j-1, "L"), (i-1, j, "U"), (i+1, j, "D")):
        if 0 <= ni < n and 0 <= nj < m and map[ni][nj] == 0 and (ni, nj) not in visited:
            visited.add((ni, nj))
            cameFrom[(ni, nj)] = ((i, j), c)
            openSet.append((ni, nj))
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: TIME LIMIT EXCEEDED

Test 10

Verdict: TIME LIMIT EXCEEDED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: TIME LIMIT EXCEEDED