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Santiago
@svpino 5 years, 4 months ago 873 views

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11 short programming problems to stretch your imagination and make sure you are staying on your toes.

(Starting with the simple ones, they get more fun as you move towards the end.)

🧵👇

1. Write a function that reverses an array in place.

In other words, the function should not use an auxiliary array to do the work.

2. Write a function that finds the missing number in an unsorted array containing every one of the other 99 numbers ranging from 1 to 100.

3. Write a function that finds the duplicate number in an unsorted array containing every number from 1 to 100.

Only one of the numbers will appear twice.

4. Write a function that removes every duplicate value in an array.

There could be more than one value duplicated. You should remove all of them leaving a single copy of the value.

5. Write a function that finds the largest and smallest number in an unsorted array.

6. Write a function that finds a subarray whose sum is equal to a given value.

7. Write a function that finds the contiguous subarray of a given size with the largest sum.

8. Write a function that, given two arrays, finds the longest common subarray present in both of them.

9. Write a function that, given two arrays, finds the length of the shortest array that contains both input arrays as subarrays.

10. Write a function that, given an array, determines if you can partition it in two separate subarrays such that the sum of elements in both subarrays is the same.

11. Write a function that, given an array, divides it into two subarrays, such as the absolute difference between their sums is minimum.

I'd love to see some answers!

If you want more content on software engineering, machine learning, and adjacent topics, give me a follow. I post threads like this every week. You can enjoy more of this content here: @svpino.

More from Santiago

Santiago
@svpino

11 key concepts of Machine Learning.

— Supervised Learning Edition —

🧵👇

😜

Before starting, remember that, if you follow me, one of your enemies will be immediately destroyed (and you'll get to read more of these threads, of course.)

And if you don't follow me, well, you just hurt my feelings.

😜

1. Labels

(Also referred to as "y")

The label is the piece of information that we are predicting.

For example:

- the animal that's shown in a picture
- the price of a house
- whether a message is spam or not

👇

2. Features

(Also referred to as "x")

These are the input variables to our problem. We use these features to predict the "label."

For example:

- pixels of a picture
- number of bedrooms of a house
- square footage of a house

👇

3. Samples

(This is also known as "examples.")

A sample is a particular instance of data (features or "x.") It could be "labeled" or "unlabeled."

👇

Santiago
@svpino

One of the most popular activation functions used in deep learning models is ReLU.

I asked: "Is ReLU continuous and differentiable?"

Surprisingly, a lot of people were confused about this.

Let's break this down step by step: ↓

Let's start by defining ReLU:

f(x) = max(0, x)

In English: if x <= 0, the function will return 0. Otherwise, the function will return x.

If you draw this function, you'll get the attached chart.

Notice there are no discontinuities in the function.

This should be enough to answer half of the original question: the ReLU function is continuous.

Let's now think about the differentiable part.

A necessary condition for a function to be differentiable: it must be continuous.

ReLU is continuous. That's good, but not enough.

Its derivative should also exist for every individual point.

Here is where things get interesting.

We can compute the derivative of a function using the attached formula.

(I'm not going to explain where this is coming from; you can trust me on this one.)

We can use this formula to see whether ReLU is differentiable.

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Santiago
@svpino

I learned enough AI/ML in 12 months to change my life forever.

You can do the same, and it all starts with a killer process to learn new things.

You can steal my approach. Every detail on the latest issue of my newsletter: https://t.co/9gaenLByFb.

Make it work for you.

Santiago
@svpino

20 machine learning questions that will make you think.

(Cool questions. Not the regular, introductory stuff that you find everywhere.)

🧵👇

1. Why is it important to introduce non-linearities in a neural network?

2. What are the differences between a multi-class classification problem and a multi-label classification problem?

3. Why does the use of Dropout work as a regularizer?

👇

4. Why you shouldn't use a softmax output activation function in a multi-label classification problem when using a one-hot-encoded target?

5. Does the use of Dropout in your model slow down or speed up the training process? Why?

👇

6. In a Linear or Logistic Regression problem, do all Gradient Descent algorithms lead to the same model, provided you let them run long enough?

7. Explain the difference between Batch Gradient Descent, Stochastic Gradient Descent, and Mini-batch Gradient Descent.

👇

8. What are the advantages of Convolution Neural Networks (CNN) over a fully connected network for image classification?

9. What are the advantages of Recurrent Neural Networks (RNN) over a fully connected network when working with text data?

👇

Santiago
@svpino

My recommendations to start with machine learning math:

• Statistics 110: Probability — Harvard University
• Essence of Linear Algebra — 3Blue1Brown
• Multivariate Calculus — Coursera

Links and 3 additional free resources here: https://t.co/fEmpmRKEvJ

If you are looking for more machine learning content, give me a follow and I’ll keep your feed interesting 😉.

More from Tech

Jonas L
@jonasLyk

Wanna disable Defender when enabled Isolated Core and Tamper protection?

Its a bit more trouble- but doable, without ruining Isolated Core/Secureboot etc.

Defenders process will run as a unkillable protected service- so new tricks needed.

Here we go:

Ok- tamper protection is easy, just make .bat - run as adm:
:again
reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\WdFilter\Instances\WdFilter Instance" /v altitude /t REG_SZ /d -1 /f
goto again

Then unload minifilter with process hacker:

The registry key will be changed while the minifilter do not protect it, when tamper protection makes the driver load again it cannot attach to volumes nor protect registry keys.

Removing it will make it recreate, but invalid altitude do the trick

Notice now the service is: Protected light(antimalware)
Now we cant do anything to the service/process- not even see its open handles.

Lets start by elevating to SYSTEM- just launch a command prompt, then close process hacker- and run it again from the command prompt.
Now process hacker runs as SYSTEM

foone
@Foone

It is 2018 and this error message is a mistake from 1974.
This limitation, which is still found in the very latest Windows 10, dates back to BEFORE STAR WARS. This bug is as old as Watergate.

When this was developed, nothing had UPC codes yet because they'd just been invented.
Back when this mistake was made, There was only one Phone Company, because they hadn't been broken up yet. Ted Bundy was still on the loose. Babe Ruth's home run record was about to fall.

When this bug was developed, Wheel of Fortune hadn't yet aired. No one had seen Rocky Horror. Steven Spielberg was still a little-known directory of TV films and one box-office disappointment. SNL hadn't aired yet. The Edmund Fitzgerald was still hauling iron ore.

WHEN THIS STUPID MISFEATURE WAS INVENTED, THE GODFATHER PART II HAD JUST OPENED IN THEATERS.

So, why does this happen? So Unix (which was only 5 years old at this point) had the good idea of "everything is a file" which mean you could do things like write to sockets, pipes, the console, etc with the same commands and instructions.

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Patrick McKenzie
@patio11

Most software founders, particularly in B2B, need to get radically better at sales. @Steli , who is the best person for explaining the scrappy stages in the beginning and then building out a team with scripts and processes, wrote a guide to:

For technical founders it is irrationally, obscenely hard to reverse years of programming (ba dum bum) that sales is a value-destroying activity. Sales is CLEARLY a value-creating activity, contingent on you have a value-creating product.

The world will not drop what they are doing to adopt your work. This is particularly true in B2B, where simply building a better mousetrap won't overcome the activation energy required to get people with additional non-mice problems to prioritize changing mousetraps today.

This is very non-obvious for founders because founders are not often people who *want* to be sold to. We often come from a background where trying out tools is a bit of a fun hobby. We like looking at all the options, making charts, and ripping out partially complete tests.

"This week I unsuccessfully trialed four software options for automating that thing that has been killing us. Our actual production process remains the same as last week. Don't worry; this was a great use of time." is not a thing you want to write in a progress report to manager.

(((E. Glen Weyl)))
@glenweyl

I am grateful to @slatestarcodex for taking the time to respond to my critique of technocracy. There is a lot there to respond to and in general I think the exchange speaks for itself. However, I think there are few points where clarification is important for the exchange to be

productive, which I'll briefly address here. I suspect many fellow travelers (e.g. @audreyt @dsallentess @JohnnieM @MichelleRempel @VitalikButerin @mds49) will find the exchange fairly ironic/revealing. I'll post this as a response on this blog as well.

1. Let me start with concessions. There are many points where @slatestarcodex correctly highlights various areas where my grasp of beliefs and facts are limited or wrong, especially in the depth of my grasp of the views of the rationalist community.

I freely admit that there are serious limits to how much I've been able to research the views of people in this community and I certainly hope they are not as I characterized them, though as I will point out below many elements of @slatestarcodex's response confirm my concerns.

2. Given the last point, I fully acknowledge the danger of throwing stones lest I shatter my own glass house. However, leaving aside any blame, I think to make sense of my piece and @slatestarcodex's response requires a bit of context that clearly he lacked. First, outside

$Trung Phan \U0001f1e8\U0001f1e6$

Trung Phan 🇨🇦...
@TrungTPhan

For decades, Jeff Bezos shunned ads.

But now, Amazon’s ad business is huge: it’s on a $30B+ annual run rate (more than 2x the combined sales of Twitter, Snap and Pinterest).

Here’s how it happened 🧵

1/ Amazon doesn’t break out its ad business separately in financial filings. However, most analyst believe ads make up the majority of its “Other” revenue segment.

This figure has exploded from $1B in 2015 to a current annual run rate of ~$32B.

2/ In 2009, Bezos said “ads are the price you pay for a crappy product”.

But the business is so lucrative that Amazon’s interface has been swamped with ads:

◻️ First 3-7 search results (left in red)
◻️ Most of the product page (right in blue)

3/ Prior to the rise of ads, Amazon set out to build the ultimate organic customer recommendations engine.

The approach was codified in a famed 2003 research paper: “Amazon Recommendations: Item-to-Item Collaborative Filtering.”

4/ In recent years, Amazon organic recommendations:

◻️"Customers who bought this also bought this"
◻️"Customers who viewed also viewed"

Have been replaced w/ ads:

◻️ "Sponsored products related to"
◻️ "Brands related to this category"

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Jaya_Upadhyaya
@Jayalko1

NARHARI AND BHAGWAN PANDURANG/VITTHAL

Once a goldsmith by the name of Narhari lived in Pandharpur. He excelled in his craft. He had vowed not to look at Pandurang or visit his mandir ever, as he was a Shiva Bhakt.
One day, a wealthy merchant visited him.

He wanted a gold girdle studded with precious gems, to be made for Prabhu Vitthal. Narhari refused to make it as it was for Vitthal.
After many requests, he agreed to make the girdle but asked the merchant to bring the measurement from the mandir as he himself would not go there

The measurement was given n he made the girdle. When the girdle was put on Vitthal, it was loose. Narhari had to shorten it. Now the girdle became tight. So Narhari was forced to take measurement on his own. He had to go to the mandir but went blindfolded to avoid seeing Vitthal

In the Mandir, when blindfolded Narhari touched Vitthal, he felt as if he was touching Shiva with matted hair, the moon, snake in His neck and Trishul in His hand. Ecstatic with joy, he removed the blindfold to see Shiva but he found the murti of Vitthal with Rukmini there.

He realised the truth that there was no difference between Vitthal and Shiva. Narhari at once fell at the feet of Panduranga. He then took the measurement of the waist of Vitthal and this time the ornament fit the Murti perfectly.

Narayan Hari🙏🏻

WORLD OF SANATAN DHARM...
@world_sanatan

THE LAST STAND OF PAVAN KHIND - THE 300 BATTLE OF INDIA

A long🧵that u must read

In desperate times, great men come forth. Those men who are ready to sacrifice all of their lives work for a single cause.

Baji Prabhu Deshpande is one such man.

1/25

Battle was between the Maratha Warrior Baji Prabhu Deshpande and Sidi Masoud of Adil Shahi Sultanate.

In 1660, the Maratha King Shri Chhatrapati Shivaji was trapped in the fort of Panhala, under siege and vastly outnumbered by an Adilshahis army led by Sidi Masoud.

2/25

And while everyone is thinking that finally the Maratha king will be subdued, Shivaji planned to escape to the fort of Vishalgadh. It was administered by a Maratha chieftain named Range Narayan Orpe under Shivaji.

3/25

For months the siege warfare continued as Shivaji made sure that the food source of the Besieging army drops down, due to which they will initiate a general assault on the castle.

4/25

Shivaji, Baji Prabhu, and around 600 of their best troops, hardened mountaineers of the Maval region, would dash through the Adilshahis force at night.

A man named Shiva Kashid, who resembled Shivaji in appearance, had volunteered to dress like the king and get captured.

5/25

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SK
@sk_diary1

Kolaru Pathigam-Thevaram hymn composed by ThiruGnana Sambandar- #Thread

In Tamil Kol means planets,Aru means cut- set of songs in Kolaru Pathigam addresses all Navagrahas& last 2 lines of every song with end a plea to Bhagwan Shiva to reduce/erase the ill effects of Navagrahas

கோளறு பதிகம் - This pathigam was sung by Thirugnana Sambandar at Thirumaraikadu Kshetram -Vedaranyam,Tamilnadu

Thirugnana Sambandar & Appar(Thirunavukkarasar) travelled together to various Shiva Alayam to spread shivam & bhakti among people.They both reached Thirumaraikadu.

Thirumaraikadu(Vedaranyam) -
Appar & Sambandar were asked to enter the temple through side entrance.The main door was locked by Vedas many years ago.Appar&Sambandar sang devotional hymns praising Shiva, after which the gates opened & closed.After which main door opened for all.

After darshan of Bhagwan Shiva at Thirumaraikkadu,Sambandar received a message to travel to Madurai.
During that time, Samanam was on the rise in the Pandya Kingdom.The Pandya King converted to Samanam.The Queen Mangaiyarkkarasi was a staunch Shiva devotee and was upset.

Kularchirai Nayanar ,Chief Minister of Pandya kingdom was in agony by the turn of events.Queen requested Kulachirai Nayanar to escort Thiru gnana Sambandar to Madurai.Kularchirai Nayanar met Thiru gnana Sambandar at Thirumaraikkadu & requested him to visit Madurai.

Vibhu Vashisth
@VIBHU_Tweet

Did you know?

When Saudi Arabia's King visited India in 1955, PM Nehru ordered all the Hindu Temples and Idols of Hindu Deities that came in Saudi King's way to be covered up.
Our temples are the architectural marvels in their own league.

Each of our temples tells the story of our rich history and cultural heritage. Was Nehru that ashamed of his own nation's heritage that he had to cover them up or there was some other reason? The answer would be best known to him only.

PM Nehru invited the then Saudi King Saud bin Abdul Aziz to India who accepted the invitation and planned a 17 day long official visit to India in 1955. Saudi King had brought a large delegation with him and he had to visit various Indian cities like Mumbai, Hyderabad, Agra,

Aligarh, Shimla, Mysore and Varanasi. However, when Saudi King reached Varanasi, Nehru ordered to cover all the temples and Idols with curtains that came in the way of the Royal Convoy. During his stay in Varanasi, Govt buildings were painted with the words "Kalma Tayyiba".

'Kalma Tayyiba' means 'There is not God but only Allah and Mohammed is his messenger'. In addition to it, Pooja and Aartis were also stopped at temples. I can call it the appeasement politics of the highest order and Nehru was indeed the greatest appeaser of all times.

Brian Armstrong
@brian_armstrong

1/ Productivity tip: when I keep procrastinating on something I often trick myself by saying, "ok just work on it for the next 20 minutes" or some short period of time, "and then you can chill/relax guilt free" and give myself some treat (sugar, netflix, etc)

2/ Usually at the 20 minute mark (sometimes I set a timer) I'm so engrossed in what I'm doing that I don't want want to stop and end up working on it for the next hour or two. But getting started seems to be the hardest part.

3/ Key to this: you have to actually be ok with stopping after 20 minutes and being guilt free if that's how you feel. So it's not a trick, i have the option every time, I just often don't want to use it once i'm in the zone.