Shared code

import sys
from collections import deque

input = sys.stdin.readline


def solve(n, m, grid):
    parent = [[None] * m for _ in range(n)]
    dirs = [(0, 1, "R"), (1, 0, "D"), (-1, 0, "U"), (0, -1, "L")]

    def bfs(pos):
        lst = deque([pos])
        new_lst = deque()
        while lst:
            for i, j in lst:
                if grid[i][j] != "#":
                    grid[i][j] = "#"
                    for x, y, d in dirs:
                        a, b = i + x, j + y
                        if 0 <= a < n and 0 <= b < m and grid[a][b] != "#":
                            new_lst.append((a, b))
                            parent[a][b] = (i, j, d)
            lst = new_lst
            new_lst = deque()

    a_pos = (0, 0)
    b_pos = (0, 0)
    for i, row in enumerate(grid):
        for j, col in enumerate(row):
            if col == "A":
                a_pos = (i, j)
            elif col == "B":
                b_pos = (i, j)

    ans = 0
    bfs((a_pos[0], a_pos[1]))
    x, y = b_pos

    if parent[x][y]:
        ans = []
        while (x, y) != a_pos:
            grid[x][y] = "X"
            x, y, d = parent[x][y]
            ans.append(d)
        print("YES")
        print(len(ans))
        print("".join(reversed(ans)))
    else:
        print("NO")


def main():
    n, m = list(map(int, input().split()))
    grid = [list(input().strip()) for _ in range(n)]
    solve(n, m, grid)


main()