Shared code

import sys

input = sys.stdin.readline


def solve(n, m, grid):  # flatten grid to 1d to speed up
    parent = [None] * (n * m)
    dirs = [(0, 1, "R"), (1, 0, "D"), (-1, 0, "U"), (0, -1, "L")]

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

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

    ans = 0
    bfs(a_pos)
    x, y = divmod(b_pos, m)

    if parent[b_pos]:
        ans = []
        while (x, y) != divmod(a_pos, m):
            grid[b_pos] = "X"
            b_pos, d = parent[b_pos]
            x, y = divmod(b_pos, m)
            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 = []
    for _ in range(n):
        grid.extend(input().strip())
    solve(n, m, grid)


main()