Course Schedule

class Solution {
    int[] visited;
    List<Integer>[] list;
    public boolean canFinish(int numCourses, int[][] prerequisites) {
        if(prerequisites.length <= 1){
            return true;
        }
        list = new ArrayList[numCourses];
        for(int i = 0; i<numCourses; i++){
            list[i] = new ArrayList<>();
        }
        for(int i = 0; i<prerequisites.length; i++){
            list[prerequisites[i][1]].add(prerequisites[i][0]);
        }
        //System.out.println(Arrays.toString(list));
        visited = new int[numCourses];
        for(int i = 0; i<numCourses; i++){
            if(hasCycle(i)){
                return false;
            }
        }
        return true;
    }
    public boolean hasCycle(int u){
        if(visited[u] == 1){
            return true;
        }
        if(visited[u] == 2){
            return false;
        }
        
        visited[u] = 1;
        for(int i = 0; i<list[u].size(); i++){
            if(hasCycle(list[u].get(i))){
                return true;
            }
        }
        visited[u] = 2;
        return false;
    }
}