Abandoned warehouse

import sys
from collections import deque


def main():

    input = sys.stdin.readline

    n, m = map(int, input().split())
    inpt = []
    for _ in range(n):
        inpt.append(input().rstrip("\n"))

    start_node = (0, 0)
    exit_node = (0, 0)

    for i in range(1, n):
        row = inpt[i]
        j = row.find("A")
        if j >= 0:
            start_node = (i, j)
        j = row.find("B")
        if j >= 0:
            exit_node = (i, j)

    moves = [
        (1, 0),
        (-1, 0),
        (0, 1),
        (0, -1),
    ]

    q = deque([start_node])
    prev = [-1] * (n * m)

    found = False
    while q:
        i, j = q.popleft()
        if (i, j) == exit_node:
            found = True
            break
        for ii, jj in moves:
            prv = i * m + j
            if 0 <= i + ii < n and 0 <= j + jj < m and inpt[i + ii][j + jj] != "#":
                ix = (i + ii) * m + (j + jj)
                if prev[ix] == -1:
                    prev[ix] = prv
                    q.append((i + ii, j + jj))

    if found:
        print("YES")
        node = exit_node[0] * m + exit_node[1]
        sn = start_node[0] * m + start_node[1]
        trace = [node]
        while node != sn:
            node = prev[node]
            trace.append(node)
        print(len(trace) - 1)

        node = trace.pop()
        out = ""
        while len(trace) > 0:
            next = trace[-1]
            if next > node:
                if next == node + 1:
                    out += "R"
                else:
                    out += "D"
            else:
                if next == node - 1:
                    out += "L"
                else:
                    out += "U"
            node = trace.pop()
        print(out)
    else:
        print("NO")


main()

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: WRONG ANSWER

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: WRONG ANSWER

Test 12

Verdict: ACCEPTED

Test 13

Verdict: WRONG ANSWER

Test 14

Verdict: WRONG ANSWER

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED