Course Schedule

public class Solution {
public boolean canFinish(int numCourses, int[][] prerequisites) {
    if(prerequisites == null){
        throw new IllegalArgumentException("illegal prerequisites array");
    }
 
    int len = prerequisites.length;
 
    if(numCourses == 0 || len == 0){
        return true;
    }
 
    // counter for number of prerequisites
    int[] pCounter = new int[numCourses];
    for(int i=0; i<len; i++){
        pCounter[prerequisites[i][0]]++;
    }
 
    //store courses that have no prerequisites
    LinkedList<Integer> queue = new LinkedList<Integer>();
    for(int i=0; i<numCourses; i++){
        if(pCounter[i]==0){
            queue.add(i);
        }
    }
 
    // number of courses that have no prerequisites
    int numNoPre = queue.size();
 
    while(!queue.isEmpty()){
        int top = queue.remove();
        for(int i=0; i<len; i++){
            // if a course's prerequisite can be satisfied by a course in queue
            if(prerequisites[i][1]==top){
                pCounter[prerequisites[i][0]]--;
                if(pCounter[prerequisites[i][0]]==0){
                    numNoPre++;
                    queue.add(prerequisites[i][0]);
                }
            }
        }
    }
 
    return numNoPre == numCourses;
}

}
http://www.programcreek.com/2014/05/leetcode-course-schedule-java/