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0207-course-schedule.adoc

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207. Course Schedule

{leetcode}/problems/course-schedule/[LeetCode - Course Schedule^]

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.

Note:

  1. The input prerequisites is a graph represented by a list of edges, not adjacency matrices. Read more about how a graph is represented.

  2. You may assume that there are no duplicate edges in the input prerequisites.

思路分析

TODO: 研究一下图相关算法和拓扑排序。

拓扑排序通常用来“排序”具有依赖关系的任务。

拓扑排序出来的结果是应该不是有序（升序或降序）。只是一个前后顺序。

一刷
link:{sourcedir}/_0207_CourseSchedule.java[role=include]
二刷
link:{sourcedir}/_0207_CourseSchedule_2.java[role=include]

思考题：参考资料中提到，表示图可以使用"邻接矩阵"和"邻接表"。尝试使用邻接表来重新实现。