210. Course Schedule II

public class Solution {
    public int[] findOrder(int numCourses, int[][] prerequisites) {
        int[] indegrees=new int[numCourses];
        int[] order=new int[numCourses];
        int k=0;
        Queue<Integer> queue=new LinkedList<>();
        for(int[] pair:prerequisites){
            indegrees[pair[0]]++;
        }
        for(int i=0;i<numCourses;i++){
            if(indegrees[i]==0){
                queue.offer(i);
                order[k++]=i;
            }
        }
        while(!queue.isEmpty()){
            int course=queue.poll();
            for(int[] pair:prerequisites){
                if(pair[1]==course){
                    indegrees[pair[0]]--;
                    if(indegrees[pair[0]]==0){
                        queue.offer(pair[0]);
                        order[k++]=pair[0];
                    }
                }
            }
        }
        return (k == numCourses) ? order : new int[0];
    }
}