Abandoned warehouse

from collections import deque

inp = input().split(" ")

r, c = (int(inp[0]), int(inp[1]))

map = [[] for _ in range(r)]
seen = [[(-1, -1) for _ in range(c)] for _ in range(r)]

start = (0, 0)
end = (0, 0)

translate = {".": 1, "#": 2, "A": 3, "B": 4}

for i in range(r):
    line = list(input())
    for j in range(len(line)):
        map[i].append(translate[line[j]])
        if line[j] == "A":
            start = (i, j)
        elif line[j] == "B":
            end = (i, j)

# perform bfs on the map
seen[start[0]][start[1]] = (-2, -2)
q = deque([start])

q.append(start)

while q:
    cur = q.popleft()

    cur_y, cur_x = cur

    if map[cur_y][cur_x] == 4:
        print("YES")

        directions = []

        # construct string
        run = True
        while cur_x != start[1] or cur_y != start[0]:
            previous = seen[cur_y][cur_x]
            if previous[0] - cur_y == 1:
                directions.append("U")
            elif previous[0] - cur_y == -1:
                directions.append("D")
            elif previous[1] - cur_x == 1:
                directions.append("L")
            elif previous[1] - cur_x == -1:
                directions.append("R")

            cur_x = previous[1]
            cur_y = previous[0]

        directions.reverse()

        print(len(directions))
        print("".join(directions))
        quit()

    # check up
    if (
        cur_y - 1 >= 0
        and seen[cur_y - 1][cur_x][0] == -1
        and (map[cur_y - 1][cur_x] == 1 or map[cur_y - 1][cur_x] == 4)
    ):
        seen[cur_y - 1][cur_x] = (cur_y, cur_x)
        q.append((cur_y - 1, cur_x))
    # check left
    if (
        cur_x - 1 >= 0
        and seen[cur_y][cur_x - 1][0] == -1
        and (map[cur_y][cur_x - 1] == 1 or map[cur_y][cur_x - 1] == 4)
    ):
        seen[cur_y][cur_x - 1] = (cur_y, cur_x)
        q.append((cur_y, cur_x - 1))
    # check down
    if (
        cur_y + 1 < r
        and seen[cur_y + 1][cur_x][0] == -1
        and (map[cur_y + 1][cur_x] == 1 or map[cur_y + 1][cur_x] == 4)
    ):
        seen[cur_y + 1][cur_x] = (cur_y, cur_x)
        q.append((cur_y + 1, cur_x))
    # check right
    if (
        cur_x + 1 < c
        and seen[cur_y][cur_x + 1][0] == -1
        and (map[cur_y][cur_x + 1] == 1 or map[cur_y][cur_x + 1] == 4)
    ):
        seen[cur_y][cur_x + 1] = (cur_y, cur_x)
        q.append((cur_y, cur_x + 1))

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