(Medium) Leetcode 207.Course Schedule

There is a total of n courses you have to take, labeled from 0 to n - 1 .

Some courses May has 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, are it possible for your to finish all courses?

For example:

2, [[1,0]]

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

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

There is a total of 2 courses to take. To take course 1 should has finished course 0, and to take course 0 you should also has finished course 1. So it is impossible.

Note:
The input prerequisites is a graph represented by a list of edges, not adjacency matrices. Read more on how a graph is represented.

Click to show more hints.

Solution: Topological sort topological sort

The code is as follows:

public class Solution {public boolean canfinish (int numcourses, int[][] prerequisites) {int [][]matrix=new int] [Numcourses]        [Numcourses];        int [] Indegree =new int[numcourses];        int len=prerequisites.length;            for (int i=0;i<len;i++) {int ready=prerequisites[i][0];            int pre=prerequisites[i][1];            if (matrix[pre][ready] = = 0)//prevent repeated conditions indegree[ready]++;            Matrix[pre][ready]=1;        } int count=0;        queue<integer> Queue =new LinkedList ();        for (int i=0;i<indegree.length;i++) {if (indegree[i]==0) queue.offer (i);            } while (!queue.isempty ()) {int course=queue.poll ();            count++;                        for (int i=0;i<numcourses;i++) {if (matrix[course][i]!=0) {if (--indegree[i]==0) {                    Queue.offer (i); }}}} return Count==numcourses; }}

Operation Result:

(Medium) Leetcode 207.Course Schedule