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]

Given the total number of courses and a list of prerequisite pairs, is it possible for you to finish all courses?

For example:

2, [[1,0]]

There are a total of 2 courses to take. To take course 1 you should have finished course 0. So it is possible.

2, [[1,0],[0,1]]

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.

DFS Accepted##

这是一个非常典型的拓扑排序问题,整个问题可以总结为如何判断有向图是否有环。通过对图上的每一个点做DFS,如果都是无环的,则能证明课程安排是合理的。注意,点的状态有三种,分别是没被访问,第一次访问后以及第二次访问后。

class Solution {
public:
bool canFinish(int numCourses, vector<pair<int, int>>& prerequisites) {
vector<set<int>> graph(numCourses);
bool cycle = false;
for (auto prev : prerequisites) {
graph[prev.second].insert(prev.first);
}
vector<int> visited(numCourses, 0);
for (int i = 0; i < numCourses; i++) {
if (cycle) return false;
if (visited[i] == 0) dfs(i, graph, visited, cycle);
}
return !cycle;
} void dfs(int nodei, vector<set<int>> &graph, vector<int> &visited, bool &cycle) {
if (visited[nodei] == 1) {
cycle = true;
return;
}
visited[nodei] = true;
for (auto i : graph[nodei]) {
dfs(i, graph, visited, cycle);
if (cycle) return;
}
visited[nodei] = 2;
}
};

LN : leetcode 207 Course Schedule的更多相关文章

  1. LeetCode - 207. Course Schedule

    207. Course Schedule Problem's Link ---------------------------------------------------------------- ...

  2. Java for LeetCode 207 Course Schedule【Medium】

    There are a total of n courses you have to take, labeled from 0 to n - 1. Some courses may have prer ...

  3. [LeetCode] 207. Course Schedule 课程安排

    There are a total of n courses you have to take, labeled from 0 to n - 1. Some courses may have prer ...

  4. [LeetCode] 207. Course Schedule 课程清单

    There are a total of n courses you have to take, labeled from 0 to n-1. Some courses may have prereq ...

  5. (medium)LeetCode 207.Course Schedule

    There are a total of n courses you have to take, labeled from 0 to n - 1. Some courses may have prer ...

  6. LeetCode 207. Course Schedule(拓扑排序)

    题目 There are a total of n courses you have to take, labeled from 0 to n - 1. Some courses may have p ...

  7. [LeetCode] 207. Course Schedule 课程表

    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&g ...

  8. [leetcode]207. Course Schedule课程表

    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). /* ...

  9. Java for LeetCode 210 Course Schedule II

    There are a total of n courses you have to take, labeled from 0 to n - 1. Some courses may have prer ...

随机推荐

  1. Nginx教程收集

    学习要系统,最推荐的方式是看书. 下面是收集的一些Nginx教程: https://www.gitbook.com/book/yinsigan/nginx/details http://www.ngi ...

  2. Servlet的Cookies处理

    以下内容引用自http://wiki.jikexueyuan.com/project/servlet/cookies-handling.html: Cookies是存储在客户端计算机上的文本文件,用于 ...

  3. Python学习系列之面向对象

    概述 一.Python编程方式 面向过程编程:根据业务逻辑从上到下磊代码 面向函数编程:将某功能代码封装到函数中,将来直接调用即可,无需重新写 面向对象编程:对函数进行分类.封装 二.面向过程编程 w ...

  4. Vue中-下拉框可以选择可以填写

    <el-form-item label="方法名称"> <el-autocomplete popper-class="my-autocomplete&q ...

  5. A* Pathfinding Project (Unity A*寻路插件) 使用教程

    Unity4.6 兴许版本号都已经内置了寻路AI了.之前的文章有介绍 Unity3d 寻路功能 介绍及项目演示 然而两年来项目中一直使用的是 A* Pathfinding 这个插件的.所以抽时间来写下 ...

  6. 面试题之strcpy/strlen/strcat/strcmp的实现

    阿里的电面要我用C/C++实现一个字符串拷贝的函数,虽然以前写过 strcpy 的函数实现,但时间过去很久了,再加上有点紧张,突然就措手不及了.最后写是写出来了,但没考虑异常的情况,面试官好像很不满意 ...

  7. Mac OS X 10.10, Eclipse+ADT真机调试代码时,Device Chooser中不显示真机的解决方式

    Mac OS X 10.10的环境下.Eclipse+ADT,进行真机调试时,会出现一个问题. Device Chooser对话框里不显示真机设备,仅仅有又一次插拔数据线才干够. 经过測试.有两个暂时 ...

  8. 2013级C++第12周(春)项目——成员的訪问属性、多重继承

    课程首页在:http://blog.csdn.net/sxhelijian/article/details/11890759,内有完整教学方案及资源链接 第一部分 程序阅读 1.阅读程序.分析类中成员 ...

  9. 服务器无法处理请求。 ---> 未将对象引用设置到对象的实例

    服务器无法处理请求. ---> 未将对象引用设置到对象的实例. 简短说下我遇到的问题.webservice部署到服务器上后,访问方法报上面的错误,最终原因为改方法需要操作文件夹,加上了相应的权限 ...

  10. Cocos2d-x项目创建

    以创建HelloWorld项目为例子,执行create_project.py脚本,进入Doc界面输入下面的命令: (1)E:   (切换盘符,因为我的Cocos2d-x源码在E盘,create_pro ...