Course Schedule30 Nov 2019
There are a total of n courses you have to take, labeled from
Some courses may have prerequisites, for example to take course 0 you have to first take course 1, which is expressed as a pair:
Given the total number of courses and a list of prerequisite pairs, is it possible for you to finish all courses?
Input: 2, [[1,0]] Output: true Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So it is possible.
Input: 2, [[1,0],[0,1]] Output: false Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0, and to take course 0 you should also have finished course 1. So it is impossible.
This is a topological sort problem. You can first construct the graph using each edges. And calculate indegree for each course. Once it is finished. You can push all 0-indegree courses into a queue. Keep poll the queue, and find all the related courses for this course, –indegree. Increase the count, And put the 0-indegree course into it.