解题思路：

class Solution {public boolean canFinish(int numCourses, int[][] prerequisites) {int[] inDegree = new int[numCourses];//存每个结点的入度List<List<Integer>> res = new ArrayList<>();//存结点之间依赖关系Queue<Integer> queue = new LinkedList<>();//初始化二维List集合for(int i = 0; i < numCourses; i++)res.add(new ArrayList<>());//取出每一对结点for(int[] temp : prerequisites){inDegree[temp[0]]++;res.get(temp[1]).add(temp[0]);}//先把所有入度为0的结点加入队列for(int i = 0; i < numCourses; i++)if(inDegree[i] == 0) queue.add(i);while(!queue.isEmpty()){int pre = queue.poll();numCourses--;//根据依赖关系，把入度-1for(int cur : res.get(pre)){if(--inDegree[cur] == 0)queue.add(cur);}}return numCourses == 0;}
}