Abandoned warehouse

import sys 
from collections import deque

def solve():
    input_data = sys.stdin.read().split()
    if not input_data:
        return
    
    n = int(input_data[0])
    m = int(input_data[1])

    grid = input_data[2 : 2+n]

    start_r = start_c = -1
    end_r = end_c = -1

    for i in range(n):
        for j in range(m): 
            if grid[i][j] == 'A':
                start_r, start_c = i, j
            elif grid[i][j] == 'B':
                end_r, end_c = i, j

    queue = deque([(start_r, start_c)])
    
    parent = [[None] * m for _ in range(n)]
    parent[start_r][start_c] = (-1, -1, '')

    moves = [(-1, 0, 'U'), (1, 0, 'D'), (0, -1, 'L'), (0, 1, 'R')]
    
    found = False

    while queue:
        r, c = queue.popleft() 
        
        if (r, c) == (end_r, end_c):
            found = True
            break
            
        for dr, dc, move_char in moves:
            nr, nc = r + dr, c + dc

            if 0 <= nr < n and 0 <= nc < m: 
                if grid[nr][nc] != '#' and parent[nr][nc] is None: 
                    parent[nr][nc] = (r, c, move_char)
                    queue.append((nr, nc))

    if not found: 
        print('NO')
    else:
        print('YES')
        path = []
        curr_r, curr_c = end_r, end_c
        
        while (curr_r, curr_c) != (start_r, start_c):
            prev_r, prev_c, char = parent[curr_r][curr_c]
            path.append(char)
            curr_r, curr_c = prev_r, prev_c
        path.reverse()
        print(len(path))
        print("".join(path))

if __name__ == '__main__':
    solve()

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