题目：

思路：
https://www.jianshu.com/p/25868371ddfc/

代码：

public boolean canFinish(int numCourses, int[][] prerequisites) {
        // 入度
        int[] indegress = new int[numCourses];

        // 每个点对应的边,出边
        Map<Integer, List<Integer>> adjacency = new HashMap<>();

        Queue<Integer> queue = new LinkedList<>();

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

        for (int[] cp : prerequisites) {
            indegress[cp[0]]++;
            adjacency.get(cp[1]).add(cp[0]);
        }

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

        // BFS
        while (!queue.isEmpty()) {
            Integer pre = queue.poll();
            numCourses--;
            for (int cur : adjacency.get(pre)) {
                if (--indegress[cur] == 0) {
                    queue.offer(cur);
                }
            }
        }

        return numCourses == 0;
    }