Course Schedule
30 Nov 2019Course Schedule
Description
There are a total of n courses you have to take, labeled from 0
to n-1
.
Some courses may have prerequisites, for example to take course 0 you have to first take course 1, which is expressed as a pair: [0,1]
Given the total number of courses and a list of prerequisite pairs, is it possible for you to finish all courses?
Example 1:
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.
Example 2:
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.
Explain
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.