Abandoned warehouse

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

graph = []
visited = [[False]*m for _ in range(n)]
def valid(x,y):
    return (0 <= x < n and 0 <= y < m and not visited[x][y] and graph[x][y] != '#' )


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'

    q = deque([(x,y)])
    goal = False
    while q:
        x,y = q.popleft()
        if graph[x][y] == 'B':
            goal = True
            break
        visited[x][y] = True

        if valid(x+1,y):
            steps[x+1][y] = 'D'
            q.append((x+1,y))

        if valid(x-1,y):
            steps[x-1][y] = 'U'
            q.append((x-1,y))

        if valid(x,y+1):
            steps[x][y+1] = 'R'
            q.append((x,y+1))

        if valid(x,y-1):
            steps[x][y-1] = 'L'
            q.append((x,y-1))
    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: TIME LIMIT EXCEEDED

Test 8

Verdict: TIME LIMIT EXCEEDED

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