Abandoned warehouse

from collections import deque
steps = []
n, m = map(int, input().split())

graph = []
visited = [[False]*m for _ in range(n)]

start_x, start_y = 0, 0

for i in range(n):
    row = list(input().strip())
    graph.append(row)
    steps.append([''] * m)
    for j in range(m):
        if row[j] == 'A':
            start_x, start_y = i, j

def bfs(x,y):
    steps[x][y] = 'X'
    visited[x][y] = True
    q = deque([(x,y)])
    
    directions = [(1, 0, 'D'), (-1, 0, 'U'), (0, 1, 'R'), (0, -1, 'L')]
    
    while q:
        x, y = q.popleft()
        if graph[x][y] == 'B':
            goal = True
            break

        for dx, dy, direction in directions:
            nx, ny = x + dx, y + dy
            if (0 <= nx < n and 0 <= ny < m and 
                not visited[nx][ny] and graph[nx][ny] != '#'):
                visited[nx][ny] = True
                steps[nx][ny] = direction
                q.append((nx, ny))
    else:
        goal = False
        
    if goal:
        #backtrack path with L, R, U, D
        path = []
        while graph[x][y] != 'A':
            path.append(steps[x][y])
            if steps[x][y] == 'D':
                x -= 1
            elif steps[x][y] == 'U':
                x += 1
            elif steps[x][y] == 'R':
                y -= 1
            elif steps[x][y] == 'L':
                y += 1
        print("YES")
        print(len(path))
        print(''.join(path[::-1]))
    else:
        print("NO")


bfs(start_x, start_y)

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