import sys
from collections import deque
dx = [0, 0, 1, -1]
dy = [1, -1, 0, 0]
def bfs(q):
while q:
x, y, s = q.popleft()
for i in range(4):
nx, ny = x + dx[i], y + dy[i]
if 0 <= nx < r and 0 <= ny < c:
if not check[nx][ny] and maze[nx][ny] == '.':
q.append((nx, ny, s))
check[nx][ny] = check[x][y] + 1
else:
if s == 'J':
return check[x][y]
r, c = map(int, input().split())
maze = [list(input()) for _ in range(r)]
check = [[0] * c for _ in range(r)]
q = deque()
for i in range(r):
for j in range(c):
if maze[i][j] == 'J':
check[i][j] = 1
q.append((i, j, 'J'))
if maze[i][j] == 'F':
check[i][j] = 1
q.appendleft((i, j, 'F'))
ans = bfs(q)
if ans:
print(ans)
else:
print("IMPOSSIBLE")
Python
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