course schedule

public boolean (int numCourses, int[][] prerequisites) {
        if (numCourses <= 1)
            return true;
        HashMap<Integer, HashSet<Integer>> graph = new HashMap<>();
        int[] inlink = new int[numCourses];
        for (int i = 0; i < prerequisites.length; ++i) {
            int u = prerequisites[i][1], v = prerequisites[i][0];
            if (graph.containsKey(u)) {
                if (graph.get(u).contains(v)) 
                    continue;
                inlink[v] += 1;
                graph.get(u).add(v);
            } else {
                HashSet<Integer> set = new HashSet<>();
                inlink[v] += 1;
                set.add(v);
                graph.put(u, set);
            }
        }
        return bfs(graph, inlink);
    }

    public boolean bfs(HashMap<Integer, HashSet<Integer>> graph, int[] inlink) {
        Queue<Integer> q = new LinkedList<>();
        for (int i = 0; i < inlink.length; ++i) {
            if (inlink[i] == 0)
                q.offer(i);
        }
        while (!q.isEmpty()) {
            int u = q.poll();
            if (graph.containsKey(u) == false) {
                continue;
            }
            for (int v : graph.get(u)) {
                inlink[v] -= 1;
                if (inlink[v] == 0) {
                    q.offer(v);
                }
            }
        }
        for (int i : inlink)
            if (i > 0)
                return false;
        return true;
    }

public int[] findOrder(int numCourses, int[][] prerequisites) {
        if (numCourses <= 1)
            return new int[1];
        HashMap<Integer, HashSet<Integer>> graph = new HashMap<>();
        int[] inlink = new int[numCourses];
        for (int i = 0; i < prerequisites.length; ++i) {
            int u = prerequisites[i][1], v = prerequisites[i][0];
            if (graph.containsKey(u)) {
                if (graph.get(u).contains(v))
                    continue;
                inlink[v] += 1;
                graph.get(u).add(v);
            } else {
                inlink[v] += 1;
                HashSet<Integer> set = new HashSet<>();
                set.add(v);
                graph.put(u, set);
            }
        }
        return bfs(graph, inlink);
    }
    public int[] bfs(HashMap<Integer, HashSet<Integer>> graph, int[] inlink) {
        int[] ans = new int[inlink.length];
        Queue<Integer> q = new LinkedList<>();
        for (int i = 0; i < inlink.length; ++i) {
            if (inlink[i] == 0)
                q.offer(i);
        }
        int index = 0;
        while (!q.isEmpty()) {
            int u = q.poll();
            ans[index++] = u;
            if (graph.containsKey(u) == false)
                continue;
            for (int i : graph.get(u)) {
                inlink[i] -= 1;
                if (inlink[i] == 0)
                    q.offer(i);
            }
        }
        for (int i : inlink) {
            if (i != 0)
                return new int[0];
        }
        return ans;
    }