def is_valid_position(n, m, x, y): if x <0 or x >= n or y < 0 or y >= m: return false return true def dfs(n, m, x, y, visited): directions = [(1, 2), (1, -2), (-1, 2), (-1, -2), (2,1), (2, -1), (-2, 1), (-2, -1)] visited[x][y] = true count = 0 for dx, dy in directions: new_x, new_y = x + dx, y + dy if is_valid_position(n, m, new_x, new_y) and not visited[new_x][new_y]: count += dfs(n, m, new_x, new_y, visited) visited[x][y] = false if count == 0: return1 if all(visited[i][j] for i in range(n) f