【拓扑排序】LeetCode 207. 课程表

题目链接

207. 课程表

思路

参考Krahets大佬的思路

代码

class Solution {
    public boolean canFinish(int numCourses, int[][] prerequisites) {
        int[] indegrees = new int[numCourses];
        List<List<Integer>> adjacency = new ArrayList<>();
        Queue<Integer> queue = new LinkedList<>();

        for(int i = 0; i < numCourses; i++){
            adjacency.add(new ArrayList<>());
        }
        // Get the indegree and adjacency of every course.
        // index 1 -> index 0
        for(int[] cp : prerequisites){
            indegrees[cp[0]]++;
            adjacency.get(cp[1]).add(cp[0]);
        }
        // Get all the courses with the indegree of 0.
        for(int i = 0; i < numCourses; i++){
            if(indegrees[i] == 0){
                queue.add(i);
            }
        }

        while(!queue.isEmpty()){
            int pre = queue.poll();
            numCourses--;
            for(int cur : adjacency.get(pre)){
                indegrees[cur]--;
                if(indegrees[cur] == 0){
                    queue.add(cur);
                }
            }
        }

        return numCourses == 0;
    }
}

拓展

【拓扑排序】LeetCode 210. 课程表 II