Abandoned warehouse

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


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

start = None
endd = None
for i in range (n):
    s = input()

    line = [CHAR[c] for c in s]
    map[i] = line
    idx = s.find("A")
    if idx != -1:
        start = (i, idx)
    idxB = s.find("B")
    if idxB != -1:
        endd = (i, idxB)

# print(start, endd)

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

visited = set()
# visited.add(start)
nodes = set()
from collections import deque
si, js = start
ie, je = endd

openSet = deque([(si, js, "")])

while openSet:
    current = openSet.popleft()

    i, j, s = current

    if (i,j) in visited:
        continue
    visited.add((i,j))

    if i == ie and j == je:

        print("YES")
        print(len(s))
        print(s)
        break

    if not (0 <= i < n) or  not(0<= j < m):
        continue
    if map[i][j] == 1:
        continue


    # print(i,j)
    openSet.append((i,j+1, s + "R"))
    openSet.append((i,j-1, s + "L"))
    openSet.append((i-1,j, s + "U"))
    openSet.append((i+1,j, s + "D"))
else:
    print("NO")





# def dfs(i, j):
#     if (i,j) in visited:
#         return -1
#     visited.add((i,j))
#     if not (0 <= i < n) or  not(0<= j < m):
#         return -1
#     if map[i][j] == 1:
#         return -1
#     # print(i,j)
    


#     if i == ei and j == ej:
#         return ""

#     s1 = dfs(i, j+1)
#     if s != -1: return "R" + s
#     s2 = dfs(i, j-1)
#     if s != -1: return "L" + s
#     s3 = dfs(i+1, j)
#     if s != -1: return "D" + s
#     s4 = dfs(i-1, j)
#     if s != -1: return "U" + s


#     return -1

# out = dfs(si, sj)

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: RUNTIME ERROR

Traceback (most recent call last):
  File "/box/input/code.py", line 18, in <module>
    map[i] = line
IndexError: list index out of range

Test 12

Verdict: ACCEPTED

Test 13

Verdict: TIME LIMIT EXCEEDED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: TIME LIMIT EXCEEDED