210. Course Schedule II

本文介绍了一种解决课程依赖问题的方法,通过使用入度数组存储每门课程的依赖数量,然后找到所有入度为0的课程,将其加入结果数组和队列中。在队列不为空的情况下,不断移除已完成的课程并更新剩余课程的依赖数,直至完成所有课程的学习顺序安排。

摘要生成于 C知道 ,由 DeepSeek-R1 满血版支持, 前往体验 >

Description

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 1:

Input: 2, [[1,0]]
Output: [0,1]
Explanation: There are a total of 2 courses to take. To take course 1 you should have finished
course 0. So the correct course order is [0,1] .
Example 2:

Input: 4, [[1,0],[2,0],[3,1],[3,2]]
Output: [0,1,2,3] or [0,2,1,3]
Explanation: There are a total of 4 courses to take. To take course 3 you should have finished both
courses 1 and 2. Both courses 1 and 2 should be taken after you finished course 0.
So one correct course order is [0,1,2,3]. Another correct ordering is [0,2,1,3] .
Note:

The input prerequisites is a graph represented by a list of edges, not adjacency matrices. Read more about how a graph is represented.
You may assume that there are no duplicate edges in the input prerequisites.

Problem URL


Solution

给一个数组表示课程之间的依赖关系和一共有多闪门课,问能否上的了这些课。

Using indegree array to store the courses have indegree. Then get the courses which have 0 indegreee and add them into result array and queue.

While queue is not empty, poll out the course, then find it in prerequisites, minus one for courses who have indegree from it. If its indegree becomes zero, add it to result and queue.

If index of result is not equal to the num of courses, return empty array.

Code
class Solution {
    public int[] findOrder(int numCourses, int[][] prerequisites) {
        if (numCourses == 0){
            return new int[0];
        }
        int[] indegree = new int[numCourses];
        int[] result = new int [numCourses];
        int index = 0;
        //find the courses which need prerequisites.
        for (int i = 0; i < prerequisites.length; i++){
            indegree[prerequisites[i][0]]++;
        }
        
        //add the courses which do not need prerequisites.
        Queue<Integer> queue = new LinkedList<>();
        for (int i = 0; i < indegree.length; i++){
            if (indegree[i] == 0){
                queue.offer(i);
                result[index++] = i;
            }
        }
        //add courses to result in the order of queue.
        while(!queue.isEmpty()){
            int course = queue.poll();
            //course polled means a prerequisites course has finished, we could eliminate its indegree
            for (int i = 0; i < prerequisites.length; i++){
                if (prerequisites[i][1] == course){
                    indegree[prerequisites[i][0]]--;
                    //It means we could take this class, add it to queue and result.
                    if (indegree[prerequisites[i][0]] == 0){
                        queue.offer(prerequisites[i][0]);
                        result[index++] = prerequisites[i][0];
                    }
                }
                
            }
        }
        
        return index == numCourses ? result : new int[0];
    }
}

Time Complexity: O(n)
Space Complexity: O(n)


Review
1. 用户与身体信息管理模块 用户信息管理: 注册登录:支持手机号 / 邮箱注册,密码加密存储,提供第三方快捷登录(模拟) 个人资料:记录基本信息(姓名、年龄、性别、身高、体重、职业) 健康目标:用户设置目标(如 “减重 5kg”“增肌”“维持健康”)及期望周期 身体状态跟踪: 体重记录:定期录入体重数据,生成体重变化曲线(折线图) 身体指标:记录 BMI(自动计算)、体脂率(可选)、基础代谢率(根据身高体重估算) 健康状况:用户可填写特殊情况(如糖尿病、过敏食物、素食偏好),系统据此调整推荐 2. 膳食记录与食物数据库模块 食物数据库: 基础信息:包含常见食物(如米饭、鸡蛋、牛肉)的名称、类别(主食 / 肉类 / 蔬菜等)、每份重量 营养成分:记录每 100g 食物的热量(kcal)、蛋白质、脂肪、碳水化合物、维生素、矿物质含量 数据库维护:管理员可添加新食物、更新营养数据,支持按名称 / 类别检索 膳食记录功能: 快速记录:用户选择食物、输入食用量(克 / 份),系统自动计算摄入的营养成分 餐次分类:按早餐 / 午餐 / 晚餐 / 加餐分类记录,支持上传餐食照片(可选) 批量操作:提供常见套餐模板(如 “三明治 + 牛奶”),一键添加到记录 历史记录:按日期查看过往膳食记录,支持编辑 / 删除错误记录 3. 营养分析模块 每日营养摄入分析: 核心指标计算:统计当日摄入的总热量、蛋白质 / 脂肪 / 碳水化合物占比(按每日推荐量对比) 微量营养素分析:检查维生素(如维生素 C、钙、铁)的摄入是否达标 平衡评估:生成 “营养平衡度” 评分(0-100 分),指出摄入过剩或不足的营养素 趋势分析: 周 / 月营养趋势:用折线图展示近 7 天 / 30 天的热量、三大营养素摄入变化 对比分析:将实际摄入与推荐量对比(如 “蛋白质摄入仅达到推荐量的 70%”) 目标达成率:针对健
评论
添加红包

请填写红包祝福语或标题

红包个数最小为10个

红包金额最低5元

当前余额3.43前往充值 >
需支付:10.00
成就一亿技术人!
领取后你会自动成为博主和红包主的粉丝 规则
hope_wisdom
发出的红包
实付
使用余额支付
点击重新获取
扫码支付
钱包余额 0

抵扣说明:

1.余额是钱包充值的虚拟货币,按照1:1的比例进行支付金额的抵扣。
2.余额无法直接购买下载,可以购买VIP、付费专栏及课程。

余额充值