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Course Schedule II

MediumP2Coding

There are numCourses courses labelled 0..numCourses - 1. Each entry [a, b] of prerequisites means you must take course b before course a.

Return an order in which you can take all courses. Many orders can be valid, so return the lexicographically smallest one: whenever several courses are available, take the one with the smallest label. If it is impossible (there is a cycle), return [].

Example 1

Input
numCourses = 2, prerequisites = [[1,0]]
Output
[0,1]

Example 2

Input
numCourses = 4, prerequisites = [[1,0],[2,0],[3,1],[3,2]]
Output
[0,1,2,3]
Why
Course 0 first; then 1 and 2 are available and 1 is smaller; then 2; then 3.

Example 3

Input
numCourses = 2, prerequisites = [[0,1],[1,0]]
Output
[]

Constraints

  • 1 <= numCourses <= 2000
  • 0 <= prerequisites.length <= 5000
  • 0 <= a, b < numCourses, a != b
  • Pairs are distinct.

Hints

Run checks the 3 visible tests, Submit all 10.