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 l…

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 l…

207. Course Schedule Problem's Link ---------------------------------------------------------------------------- Mean: 给定一个有向图,判断是否存在top_sort序列. analyse: 转换为:判断是否存在环. 若存在环,肯定不能找到top_sort序列. 判环的方式有很多:SPFA,top_sort,BFS,DFS...随便选一种就行. Time complexity: O…

lc 207 Course Schedule 207 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…

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 l…

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 lis…

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 l…

题目 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…

题目: 分析: 这是一道典型的拓扑排序问题.那么何为拓扑排序? 拓扑排序: 有三件事情A,B,C要完成,A随时可以完成,但B和C只有A完成之后才可完成,那么拓扑排序可以为A>B>C或A>C>B. 总的来说,拓扑排序就是对于相互之间有先后依赖关系的事件,给出一个行之有效的序列. 图解释: 反应到图中,就是一个有向无环图可以被拓扑排序,而有环图是无法进行拓扑排序的(比如,A依赖B,B依赖C,C依赖A,三者形成了环,是没有办法完成的) 很明显“课程表”这个题目就是判断题目所给的依赖关系,…

在一个有向图中,每次找到一个没有前驱节点的节点(也就是入度为0的节点),然后把它指向其他节点的边都去掉,重复这个过程(BFS),直到所有节点已被找到,或者没有符合条件的节点(如果图中有环存在). /* 思路就是平时学习的过程,每次都学习一个最先导课程(特征就是该课程没有先导课程),学完所有课程后就成功 如果在某次遍历是发现所有课程都有先导课程,就失败退出. 用一个数组记录每个课程都有几个先导课程,用多个hashset(BFS的数据记录结构)记录该课程的后续课程有哪些, 每次学一个课程,就把该课程…