class Solution {
    public boolean canFinish(int numCourses, int[][] prerequisites) {
        if(prerequisites.length == 0)
            return true;
 
        // Step-1 Create a adjacency list
        ArrayList<ArrayList<Integer>> adj = new ArrayList<>();        
        for(int i=0; i<numCourses; i++)
        {
            adj.add(new ArrayList<>());
        }
 
        // Step-2 Fill adjacency list and indegree array
        int[] indegree = new int[numCourses];
        for(int[] edge : prerequisites)
        {
            int u = edge[1];
            int v = edge[0];
 
            adj.get(u).add(v);
            indegree[v]++;
        }
 
        // Step-3 Find courses whose indegree is 0, add it to queue
        Queue<Integer> q = new LinkedList<>();
        for(int i=0; i<indegree.length; i++)
        {
            if(indegree[i] == 0)
                q.add(i);
        }
 
        // Step-4: Process queue
        int count = 0;
        while(!q.isEmpty())
        {
            int node = q.poll();
            count++;
 
            for(int u : adj.get(node))
            {
                indegree[u]--;
                if(indegree[u] == 0)
                    q.add(u);
            }
        }
 
        // if cycle exisits then we cannot finish all courses
        if(count != numCourses)
            return false;
        return true;
    }
}