1、前言

2、思路

3、代码

class Solution {
    public int[] findOrder(int numCourses, int[][] prerequisites) {
        int[] ingreedes = new int[numCourses];
        int[] top = new int[numCourses];

        HashMap<Integer, List<Integer>> adj = new HashMap<>();
        Queue<Integer> queue = new LinkedList<>();

        for(int i = 0; i < numCourses; i++){
            adj.put(i, new ArrayList<>());
        }

        for(int[] cp : prerequisites){
            ingreedes[cp[0]] += 1;
            adj.get(cp[1]).add(cp[0]);
        }

        for(int i = 0; i < numCourses; i++){
            if(ingreedes[i] == 0){
                queue.offer(i);
            }
        }

        int j = 0;
        while(!queue.isEmpty()){
            int temp = queue.poll();
            top[j++] = temp;
            numCourses--;
            for(int i : adj.get(temp)){
                ingreedes[i] -= 1;
                if(ingreedes[i] == 0){
                    queue.offer(i);
                }
            }
        }

        return numCourses == 0 ?  top : new int[0];
    }
}