Course Schedule II

Hard~25 min

There are a total of numCourses courses you have to take, labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai, bi] indicates that you must take course bi first if you want to take course ai.

For example, the pair [0, 1] indicates that to take course 0 you have to first take course 1.

Return the ordering of courses you should take to finish all courses. If there are many valid answers, return any of them. If it is impossible to finish all courses, return an empty array.

Examples

Example 1
Input: numCourses = 4, prerequisites = [[1, 0], [2, 0], [3, 1], [3, 2]]
Output: [0, 1, 2, 3]
Explanation: Course 0 has no prerequisites. Courses 1 and 2 both require course 0. Course 3 requires both 1 and 2. One valid ordering is [0, 1, 2, 3].
Example 2
Input: numCourses = 2, prerequisites = [[1, 0], [0, 1]]
Output: []
Explanation: Course 0 requires course 1, and course 1 requires course 0. This is a cycle, so no valid ordering exists.
Example 3
Input: numCourses = 1, prerequisites = []
Output: [0]
Explanation: There is only one course with no prerequisites.

Constraints

  • 1 <= numCourses <= 2000
  • 0 <= prerequisites.length <= numCourses * (numCourses - 1)
  • prerequisites[i].length == 2
  • 0 <= ai, bi < numCourses
  • ai != bi
  • All the pairs [ai, bi] are distinct
  • Expected time complexity: O(V + E)
Code
Ctrl+EnterRun|Ctrl+⇧+EnterSubmit
Output

Run your code to see results

Use Cmd+Enter to run