**Course Schedule II** ===================== ### Problem Statement Given a schedule of courses with their prerequisites, return the order in which they can be finished. If a valid order exists, you must return the correct order; otherwise, return an empty array. Each course is represented as `(course, prerequisites)`, where `(course, prerequisites[i])` means `course` is a prerequisite of `prerequisites[i]`. The same course may not be offered more than once but can be taken in any order. There may be multiple course schedules for a given graph. This problem is a variation of the [Topological Sort](https://en.wikipedia.org/wiki/Topological_sorting) problem. However, in this case, if there's a cycle in the graph, we should return an empty array, as a valid order may not exist. ### Rules and Constraints * `1 <= course1.length == course2.length <= 20` * `0 <= prerequisite <= course.length - 1` * Not every course has prerequisites, but you cannot take the same course more than once. ### Input and Output * The input consists of two arrays: * `course`: an array of strings representing the courses * `prerequisites`: an array of arrays of integers, where each inner array contains course indices that are prerequisites of the corresponding course * The output should be an array of integers representing the order in which the courses can be finished. If a valid order does not exist, the output array will be empty. ### Example **Input:** {"input_data":[1,2,3]} **Output:** [1,2,3]