[LeetCode/LintCode] Course Schedule II

Lavender 发布于2019-08-15 17:49 / 2878人阅读

Problem

There are a total of n courses you have to take, labeled from 0 to n - 1.
Some courses may have prerequisites, for example to take course 0 you have to first take course 1, which is expressed as a pair: [0,1]

Given the total number of courses and a list of prerequisite pairs, return the ordering of courses you should take to finish all courses.

There may be multiple correct orders, you just need to return one of them. If it is impossible to finish all courses, return an empty array.

Example

Given n = 2, prerequisites = [[1,0]]
Return [0,1]

Given n = 4, prerequisites = [1,0],[2,0],[3,1],[3,2]]
Return [0,1,2,3] or [0,2,1,3]

Solution

public class Solution {
    /*
     * @param n: a total of n courses
     * @param pre: a list of prerequisite pairs
     * @return: the course order
     */
    public int[] findOrder(int n, int[][] pre) {
        // write your code here
        ArrayList[] graph = new ArrayList[n];
        for (int i = 0; i < n; i++) {
            graph[i] = new ArrayList();
        }
        
        int[] indegree = new int[n];
        for (int i = 0; i < pre.length; i++) {
            graph[pre[i][1]].add(pre[i][0]);
            indegree[pre[i][0]]++;
        }
        
        Queue queue = new LinkedList();
        for (int i = 0; i < n; i++) {
            if (indegree[i] == 0) queue.add(i);
        }
        
        int[] result = new int[n];
        int index = 0;
        while (!queue.isEmpty()) {
            int node = queue.poll();
            result[index++] = node;
            ArrayList list = graph[node];
            for (int i = 0; i < list.size(); i++) {
                int cur = list.get(i);
                indegree[cur]--;
                if (indegree[cur] == 0) queue.add(cur);
            }
        }
        return index == n ? result : new int[0];
    }
}

服务器托管云服务器 Course Schedule node-schedule Schedule定时器

文章版权归作者所有，未经允许请勿转载,若此文章存在违规行为，您可以联系管理员删除。

转载请注明本文地址：https://www.ucloud.cn/yun/69467.html

210. Course Schedule II

摘要：建立入度组成，把原来输入的无规律，转换成另一种表示图的方法。找到为零的点，放到里，也就是我们图的入口。对于它的也就是指向的。如果这些的入度也变成，也就变成了新的入口，加入到里，重复返回结果。这里题目有可能没有预修课，可以直接上任意课程。 Some courses may have prerequisites, for example to take course 0 you have ...

lbool 2019-08-16 10:36 评论0 收藏0
[LeetCode] 210. Course Schedule II

Problem There are a total of n courses you have to take, labeled from 0 to n-1. Some courses may have prerequisites, for example to take course 0 you have to first take course 1, which is expressed as...

zhkai 2019-08-19 11:12 评论0 收藏0
【LC总结】图、拓扑排序 (Course Schedule I, II/Alien Dictiona

Course Schedule Problem There are a total of n courses you have to take, labeled from 0 to n - 1. Some courses may have prerequisites, for example to take course 0 you have to first take course 1, whi...

gaara 2019-08-14 15:54 评论0 收藏0
[Leetcode] Course Schedule 课程计划

Course Schedule I There are a total of n courses you have to take, labeled from 0 to n - 1.Some courses may have prerequisites, for example to take course 0 you have to first take course 1, which is e...

Amio 2019-08-14 12:40 评论0 收藏0
[LeetCode/LintCode] Number of Islands [DFS]

摘要：两个循环遍历整个矩阵，出现则将其周围相邻的全部标记为，用子函数递归标记。注意里每次递归都要判断边界。写一个的，写熟练。 Number of Islands Problem Given a boolean/char 2D matrix, find the number of islands. 0 is represented as the sea, 1 is represented as...

Fourierr 2019-08-14 15:15 评论0 收藏0