leetcode(207)课程表

课程表

解题思路：拓扑排序（实际上就是贪心算法）

class Solution {
    public boolean canFinish(int numCourses, int[][] prerequisites) {
        int len = prerequisites.length;
        if(len==0){
            return true;
        }
        int[] degree = new int[numCourses];
        for(int[] p : prerequisites){
            degree[p[0]]++;
        }
        LinkedList<Integer> list = new LinkedList<>();
        List<Integer> res = new ArrayList<>();
        for(int i=0;i<numCourses;i++){
            if(degree[i]==0){
                list.addLast(i);
            }
        }
        int temp = 0;
        while(!list.isEmpty()){
            temp = list.removeFirst();
            res.add(temp);
            for(int[] p : prerequisites){
                if(p[1]==temp){
                    degree[p[0]]--;
                    if(degree[p[0]]==0){
                        list.addLast(p[0]);
                    }
                }
            }
        }
        return res.size()==numCourses;
    }
}