Leetcode207. Course Schedule

PAT暂时没有题目练习拓扑排序，以下是Leetcode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 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.

思路1:队列方法

bool canFinish(int numCourses, vector>& prerequisites) {
    int m=prerequisites.size(),i,x=0;
    vector>g(numCourses);
    vectorin(numCourses,0);
    for(i=0;i=0&&c2>=0&&c1q;
    for(i=0;i

思路2:dfs判断DAG(Directed Acyclic Gragh)

vector>g;vectorvisit;
bool canFinish(int numCourses, vector>& prerequisites) {
    int m=prerequisites.size(),i,x=0;
    g.resize(numCourses);
    visit.resize(numCourses,0);
    for(i=0;i=0&&c2>=0&&c1