Popularity - Intro to Computer ScienceYouTube↗  IA↗(long shot)
Education  682 views 6 likes 0 dislikes   23 Feb 2015
Udacity 651K subscribers United States YouTube↗


Please select the problem
You must specify your email and describe the problem in detail
Describe your problem in detail if it's not obvious

Click to Play Video Click to Play Video
So here's a typical group of friends in middle
这里是一组典型的中学朋友圈
school. And some of the people are popular, some of
有些人非常受欢迎 有些可能
them might not be. The first step to deciding
不受欢迎 要决定谁是
who's popular, is looking at who has a lot of
受欢迎的第一步 是寻找谁有很多
friends. So let's draw in some links, that show
朋友 因此让我们画一些连线 显示
who's a friend. And friendship links are one directional. Just
谁是朋友 而且朋友关系连线是单向的
because Alice's friends with Bob, doesn't mean that Bob
因为 Alice 的朋友是 Bob 并不意味着 Bob
is friend with Alice. So we'll draw our links as
的朋友是 Alice 因此我们画出带箭头的
arrows, so this means this person, we'll call him Bob, is
连线 那么这个意味着这个人 我们叫他 Bob
friends with Alice. And let's say, Alice
是 Alice 的朋友 假设 Alice
has many friends. And let's say Bob is also friends with
有许多朋友 假设 Bob 也是这个人的
this person, they're friends with each other.
朋友 他们互相是朋友
We have lots of friendship links. Some
我们有许多朋友关系连线 有些是
of them are bi-directional but not all of them. So, we have lots of friendships.
双向的 但是并不是所有的都是 那么 我们有很多朋友关系
So, is this enough to decide who's popular. So, if you
这足够来确定谁更受欢迎吗？如果你是
went to a school like I did, it's not. Just having a
上跟我一样的学校 这并不能够确定 仅仅有
lot of friends is not enough to make you popular, you
很多朋友不能够让你变得受欢迎 你
have to have the right friends. You have to be friends with
必须有正确的朋友 你必须跟
the popular people. So, it's not enough to have lots of
受欢迎的人做朋友 因此在高中有许多奇怪的
geeky friends say in high school, you've gotta have lots of friends
朋友并不足够 你一定要有很多
that are popular. So that means the definition of popular, isn't
受欢迎的朋友 因此定义受欢迎 并不仅仅
just about having lots of friends, it's about having lots of friends,
是有许多朋友 而是有许多的朋友
who also have lots of friends. That's what
他们也有许多朋友 这是
make some one popular, so we can define
使人受欢迎的原因 因此我们可以定义
popularity of a person is the number of
一个人的受欢迎程度是 人物 P 的
people who are friends with p. This means
朋友人数 也就是说
the number of links from someone else to
从其它人到这个人的连线数量是
that person is their popularity score. So here
他们的受欢迎程度得分 这是
is Charlie, so there are one, two, three
Charlie 然后这里有一条、两条、三条
links into Charlie, so Charlie's popularity score would
连线连接到 Charlie 因此 Charlie 的受欢迎程度
be three. Alice also has three links, so her
是 3 Alice 也有 3 条线 因此她的
popularity score would also be three. Bob only has one
受欢迎程度也是 3 Bob 仅有一条
arrow going to Bob, so his popularity score would be
线连着 他的受欢迎程度就只有 1 了
one. So, this isn't a bad way to define popularity,
因此 这个定义受欢迎程度的方式并不糟糕
but it's not quite right. So, the definition of popularity
但是也并不准确 所以定义受欢迎程度
doesn't just depend on the number of friends you have,
并不取决于你有多少朋友
it depends on, both, the number, and the popularity of
它取决于 朋友数量以及你朋友
your friends. So, we can change the definition. Let's instead
受欢迎的程度 所以 你可以改变这个定义 让我们重新
define the popularity score of a person p. Now
定义人物 P 的受欢迎程度 现在
it's going to be the sum of the popularities of
我们要把他们所有朋友的
all of their friends. So we can write that in
受欢迎程度加起来 那么我们可以
a mathematical way, so using the sigma means to sum
用数学的方式写下来 使用 sigma 意味着相加
up. We're going to take each friend, that is in
我们要取出每个朋友 就是
the friends of p. And we're going to sum up the
P 的所有朋友 然后我们将要把他们的
popularity score of the friends. If the mathematical notation is
受欢迎程度累加起来 如果你对数学符号
unfamiliar to you, we could also write this as pseudo
不熟悉 我们也可以用伪 Python 代码
Python code. We're thinking of the popularity of
来写 我们正在思考人物 P 的
a person p. Let's assume we have a
受欢迎程度 让我们假设我们有一个
function that gives us the friends. So we're
函数给到我们 friends 列表 那么我们
going to start with a score of zero. We're going to
要初始化 score 为 0
loop through the friends. And for each friend,
通过循环遍历 friends 对于每一个朋友
we're going to add to p score, the popularity score
我们会将他的受欢迎程度得分 添加到
of the friend. And we'll return the score
P 的分数 然后我们将会返回 score
as the result. So now, you've seen a mathematical
作为结果 现在 你看到了一个数学方式的
definition of popularity, you've seen the same thing as code. I'm going to ask
受欢迎程度定义 你也以代码的形式看到了该定义 我接下来
you a very important quiz question next. Its an easy one to get
将要提出一个重要的测验问题 如果尝试两次
right if you try it twice because there's only two answers, but think
比较容易做对 因为仅仅有两个答案 但是
about it carefully. See if you can get it right the first time.
仔细考虑 看能不能一次答对
Similar videos:

Next Step
Udacity
26.4K views 2 likes 0 dislikes 23 Feb 2015100% match

Testing2 - Intro to Computer Science
Udacity
19.4K views 2 likes 0 dislikes 23 Feb 2015100% match

Advice from Sergey Brin - Intro to Computer Science
Udacity
31.6K views 49 likes 10 dislikes 23 Feb 2015100% match




Find Element - Intro to Computer Science
Udacity
22.1K views 19 likes 0 dislikes 29 May 2012100% match

Define nextDay - Intro to Computer Science
Udacity
21.7K views 2 likes 0 dislikes 23 Feb 2015100% match

Rounding Numbers - Intro to Computer Science
Udacity
34K views 28 likes 3 dislikes 02 Mar 2012100% match

Introduction
Udacity
87.8K views 315 likes 4 dislikes 25 Apr 2014100% match




Strings Solution - Intro to Computer Science
Udacity
19.4K views 22 likes 6 dislikes 02 Mar 2012100% match

Valid Strings - Intro to Computer Science
Udacity
35.1K views 3 likes 0 dislikes 23 Feb 2015100% match

Break - Intro to Computer Science
Udacity
22K views 24 likes 0 dislikes 02 Mar 2012100% match

Proc - Intro to Computer Science
Udacity
16.7K views 17 likes 1 dislikes 23 Feb 2015100% match

Countries - Intro to Computer Science
Udacity
20K views 23 likes 0 dislikes 29 May 2012100% match

Python Programming 2 - Intro to Computer Science
Udacity
30.1K views 24 likes 0 dislikes 02 Mar 2012100% match

Inc Procedure - Intro to Computer Science
Udacity
18.9K views 26 likes 1 dislikes 02 Mar 2012100% match

Replace Spy - Intro to Computer Science
Udacity
20.7K views 13 likes 0 dislikes 29 May 2012100% match

Testing2 Solution - Intro to Computer Science
Udacity
18.9K views 17 likes 3 dislikes 23 Feb 2015100% match

Hello!!! - Intro to Computer Science
Udacity
51K views 7 likes 0 dislikes 23 Feb 2015100% match

Eat Quiz Solution - Intro to Computer Science
Udacity
21K views 16 likes 0 dislikes 23 Feb 2015100% match

What Is a Program - Intro to Computer Science
Udacity
22.9K views 26 likes 1 dislikes 23 Feb 2015100% match

Return Statement - Intro to Computer Science
Udacity
18.3K views 11 likes 4 dislikes 23 Feb 2015100% match

Python Programming 1 - Intro to Computer Science
Udacity
47.7K views 33 likes 0 dislikes 02 Mar 2012100% match


Simple Mechanical Algorithm - Intro to Computer Science
Udacity
24.9K views 3 likes 1 dislikes 23 Feb 2015100% match

Language Ambiguity
Udacity
97.8K views 34 likes 0 dislikes 23 Feb 2015100% match

Popularity - CS101 - Udacity
Udacity
880 views 8 likes 0 dislikes 02 Jun 201294% match

Biggest - Intro to Computer Science
Udacity
30.2K views 28 likes 0 dislikes 02 Mar 201278% match

Testing - Intro to Computer Science
Udacity
31.4K views 6 likes 0 dislikes 23 Feb 201578% match

Abbaize - Intro to Computer Science
Udacity
30.6K views 32 likes 0 dislikes 02 Mar 201278% match

Index - Intro to Computer Science
Udacity
26.9K views 37 likes 1 dislikes 29 May 201278% match

Median - Intro to Computer Science
Udacity
30K views 21 likes 0 dislikes 23 Feb 201578% match

Square - Intro to Computer Science
Udacity
32.5K views 32 likes 0 dislikes 02 Mar 201278% match


Settings Privacy About Contact Donate