算法：拓扑排序-课程表

class Solution {

    public boolean canFinish(int numCourses, int[][] prerequisites) {
        List<Integer>[] arr = new ArrayList[numCourses];
        int[] inDegree = new int[numCourses];
        for(int i=0; i<numCourses; i++) {
            arr[i] = new ArrayList<Integer>();
        }
        for(int i=0; i<prerequisites.length; i++) {
            arr[prerequisites[i][0]].add(prerequisites[i][1]);
            inDegree[prerequisites[i][1]]++;
        }
        Stack<Integer> stack = new Stack<>();
        for(int i=0; i<numCourses; i++) {
            if(inDegree[i] == 0) {
                stack.push(i);
            }
        }
        int cnt = 0;
        while(!stack.isEmpty()) {
            int del = stack.pop();
            cnt++;
            for(int i=0; i<arr[del].size(); i++) {
                int tmp = arr[del].get(i);
                inDegree[tmp]--;
                if(inDegree[tmp] == 0) {
                    stack.push(tmp);
                }
            }
        }
        return cnt == numCourses;
    }

}