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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.

public class Solution {    public boolean canFinish(int numCourses, int[][] prerequisites) {        Map
   
    > map = new HashMap
    
     >();		int[] indegree = new int[numCourses];		Queue
     
       queue = new LinkedList
      
       ();		int count = numCourses;		for (int i = 0; i < numCourses; i++) {			map.put(i, new ArrayList
       
        ());		}		for (int i = 0; i < prerequisites.length; i++) {			map.get(prerequisites[i][0]).add(prerequisites[i][1]);			indegree[prerequisites[i][1]]++;		}		for (int i = 0; i < numCourses; i++) {			if (indegree[i] == 0) {				queue.offer(i);			}		}		while (!queue.isEmpty()) {			int current = queue.poll();			for (int i : map.get(current)) {				if (--indegree[i] == 0) {					queue.offer(i);				}			}			count--;		}		return count == 0;    }}
       
      
     
    
   

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