BC TECH
Saved by @SteveeRogerr

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
Santiago
@svpino
You gotta think about this one carefully!

Imagine you go to the doctor and get tested for a rare disease (only 1 in 10,000 people get it.)

The test is 99% effective in detecting both sick and healthy people.

Your test comes back positive.

Are you really sick? Explain below 👇

The most complete answer from every reply so far is from Dr. Lena. Thanks for taking the time and going through


You can get the answer using Bayes' theorem, but let's try to come up with it in a different —maybe more intuitive— way.

👇


Here is what we know:

- Out of 10,000 people, 1 is sick
- Out of 100 sick people, 99 test positive
- Out of 100 healthy people, 99 test negative

Assuming 1 million people take the test (including you):

- 100 of them are sick
- 999,900 of them are healthy

👇

Let's now test both groups, starting with the 100 people sick:

▫️ 99 of them will be diagnosed (correctly) as sick (99%)

▫️ 1 of them is going to be diagnosed (incorrectly) as healthy (1%)

👇
HEALTH
Santiago
Santiago
@svpino
My recommendation to start learning how to deal with structured data: Kaggle's Pandas Tutorial.

• Creating, Reading, Writing
• Indexing, Selecting, Assigning
• Summary Functions, Maps
• Grouping, Sorting
• Data Types, Missing Values
• Renaming, Combining

100% Python 🐍.
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Santiago
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.
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Santiago \U0001f1fa\U0001f1f8\U0001f1fa\U0001f1e6
Santiago 🇺🇸🇺🇦...
@svpino
You are building a binary classification model to determine whether a picture shows a hot dog or not.

Which of the following activation functions is a good candidate for the output layer?

1. Rectifier Linear Unit (ReLU)
2. Leaky ReLU
3. Sigmoid
4. Softmax

Think about it.

The answer:

You could use either Sigmoid or Softmax.

I'm sure most of you picked Sigmoid. It's certainly the best way to approach this problem.

But Softmax is also an option —although unconventional for a binary classifier.

How about the other choices?

ReLU returns its input if positive, zero otherwise. Leaky ReLU is based on ReLU but with a slight slope for negative values.

ReLU and Leaky ReLU will always give us the previous layer output with no modifications if the input is always positive.

This doesn't help us.

Sigmoid has the ability to squash its input into a range that goes from 0 to 1.

This is good because we can now set a specific threshold for the output of a binary classifier.

Here is an example.

Any image with an output equal to or under 0.5 doesn't show a hot dog. Any image with an output above 0.5 shows a hot dog.

Sigmoid makes it very easy.

How about Softmax?
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Santiago
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 😉.
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EverythingOppresses
EverythingOppresses
@SoOppressed
The first area to focus on is diversity. This has become a dogma in the tech world, and despite the fact that tech is one of the most meritocratic industries in the world, there are constant efforts to promote diversity at the expense of fairness, merit and competency. Examples:

USC's Interactive Media & Games Division cancels all-star panel that included top-tier game developers who were invited to share their experiences with students. Why? Because there were no women on the

ElectronConf is a conf which chooses presenters based on blind auditions; the identity, gender, and race of the speaker is not known to the selection team. The results of that merit-based approach was an all-male panel. So they cancelled the conference.

Apple's head of diversity (a black woman) got in trouble for promoting a vision of diversity that is at odds with contemporary progressive dogma. (She left the company shortly after this

Also in the name of diversity, there is unabashed discrimination against men (especially white men) in tech, in both hiring policies and in other arenas. One such example is this, a developer workshop that specifically excluded men: https://t.co/N0SkH4hR35
TECH
Guillaume Chaslot
Guillaume Chaslot
@gchaslot
The YouTube algorithm that I helped build in 2011 still recommends the flat earth theory by the *hundreds of millions*. This investigation by @RawStory shows some of the real-life consequences of this badly designed AI.


This spring at SxSW, @SusanWojcicki promised "Wikipedia snippets" on debated videos. But they didn't put them on flat earth videos, and instead @YouTube is promoting merchandising such as "NASA lies - Never Trust a Snake". 2/


A few example of flat earth videos that were promoted by YouTube #today:
https://t.co/TumQiX2tlj 3/

https://t.co/uAORIJ5BYX 4/

https://t.co/yOGZ0pLfHG 5/
TECH , FLAT EARTH
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Venkatesh Rao
Venkatesh Rao
@vgr
There are only 3 real challenges to free speech at the tech level a) the need for CDNs at scale b) distortions of net neutrality c) nation-state firewalls.

All other claims are about social governance on private sites, where applying free speech doctrine is a stretch at best

Baseline free speech has expanded modestly since 1776 or whatever your reference point is.

About 20% beyond core case of government-critical speech in formally public spaces and media I'd say.

You can (for example) have more kinds of conversations in a bar without getting punched or kicked out by other patrons or management. You can teach more things in colleges than 100 years ago.

That's a genuine de facto increase in practical, informal free speech/expression.

But online free "speech" is, as @reneed has pointed out, not an expansion of free speech at all, but an expansion of reach. It is like the secondary freedom of the press to print as many copies as they can afford, not primary freedom to say what they want

If a newspaper wants to print more copies it has buy more printing equipment and front more upfront costs. Reach for a paper publication is not "free", but a function of desired circulation, which in turn is a function of demand prediction etc. But that logic is obscured online.
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HankHeIl
HankHeIl
@HankHeil
So we had to develop technologies like this to barely manage control over limited areas in Iraq's few urban centers. Only ~8 in 100 Iraqi adults owns a personal vehicle. That rate is > 1 car/adult in America yet I have never seen any doctrine paper or work of fiction address this


We've seen and struggled in civil conflicts with instant, local, universal, distributed communications (cell phone era, basically every conflict since 2000). We've seen and struggled in conflicts with instant, global, universal distributed communications (everything since 2011).

The world's most overfunded military and glow in the dark agencies struggle and largely fail to contain conflicts where fhe vast, vast majority of people are locked into a ~5mi radius of their home.

How can they possibly contain a conflict in a nation with universal car ownership and the most developed road network in the world? The average car can travel over 400 miles on one tank of gas, how can you contain the potential of that kind of mobility?

I think that's partially why the system was so freaked out by 1/6. Yes, most of it is histrionics but you don't decide to indefinitely turn your capital into the Baghdad Green Zone with fortifications and 25k troops over histrionics alone.
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Darkroom
Darkroom
@usedarkroom
Following up last year’s surprisingly popular "10 things you likely didn’t know about Darkroom" and your many requests for more tips, we put together a second edition that focuses on workflows in Darkroom. Click through to read it all right here in this thread.

1/10 Copy & Paste your Edits in Batch. Skip the hassles of re-applying each edit over and over again by copying your edits from the tap-and-hold library menu, History tool, or the Actions (•••) menu. Go to your other photos, and paste your edits onto them.


2/10 The joy of seeing your wonderful shot in motion is why we love Live Photos so much, and why we fully support editing and exporting them! While editing, Tap the “LIVE” button at the left top when viewing a Live Photo for playback.


3/10 Turn your iPhone to landscape for an iPad like editing experience, bringing some iPad exclusive functionality to iPhone. In the library grid we show the Library Sidebar, when viewing or editing we show the Photo Strip, and in the color tool we show our Color Histogram.


4/10 Manage while editing with the Photostrip. With the photo strip available on all devices in landscape orientation, you can skip & hop through your library while editing, or quickly compare multiple photos to find the one with the perfect expression or the perfect light.
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MAHARAANI TARARANI: THE QUEEN OF MARATHAS

Rani Tarabai was the brave daughter-in-law of Chhatrapati Shivaji and one of the greatest medieval Monarchs India ever had.
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Tarabai was just 8yrs old when she was married to Shivaji's younger son, Rajaram. Mughals and Marathas were constantly at war with each other. Shivaji was crowned the ruler of the Independent Maratha Swarajya in 1674 which was established by him.


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If u are looking to enter a scrip just before the breakout
what would u look for?
How would u identify scrips just before breakout?

Here are a few pointers
Carefully understand the them and use at ur own discretion
(All comments r compiled from a question i posed)

1/23

Price is testing the same resistance repeatedly since long.
But now in recent times it's forming multiple candles near the same resistance with low volume.
Observe it and see for opposite move.
As soon as u get a positive candle, get in to it.

2/23

1. Volume buildup (vol > when resistance point created) along with, increase in OI, increase in delivery % on HTF
2. On LTF, price stalling around breakout area for at least 1-2hr.
3. No major events.

3/23

Stock reaching breakout LVL with HL-HH
Contraction of price and volume near it especially near 20 days ma.
If there is any breach of the latest HL it should be followed by a bullish candle with good volume.
Left side of the chart has a rally with a very steep slope of ma.

4/23

Number of wide range green bars with high volumes.
If stock is at its ATH then it adds more conviction bcz there wont b supply after that point

Consolidation below the resistance, volume of the candles & strong bullish candle closing at near highs just below the resistance

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foone
foone
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So there's a class of puzzles called "river crossing puzzles" which involve having to cross a river on a boat/bridge containing some set of individuals/items with restrictions on which ones can be on the boat/left on each shore, right?

and the most common subclass of these problems is the one where you have 3 items/animals to cross with.
This is alternatively called the "fox, goose, and bag of beans" or "wolf, goat, and cabbage" puzzle.

the idea is that your boat can only carry one item at a time, but if you leave the wolf/fox unattended with the goat/goose, the wolf/fox will eat the goat/goose.
and similarly, the goose/goat will eat the beans/cabbage if left alone

so you have to set up a set of actions that never leaves either side of the river in one of the lose-states.

the solution to this variant being:
1. take the goat/goose over
2. return empty
3. take the wolf/fox over
4. return with the goat/goose
5. take the cabbage/beans over
6. return empty
7. take the goat/goose over
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Sam is my middle child & he’s a terror. A “boy’s boy” as so many (not me) would say. He’s rough and tumble, he’s loud, he’s always dirty, loves trucks, plays sports and knee drops me from the couch. But he also loves a lot of “girl” things.

Sam has a collection of purses because he likes to carry things around. And he also loves to have his nails painted bright colors because he thinks they “look beautiful.” And he’s right – they are beautiful…


So he proudly wore his red nail polish to kindergarten this morning because Sam has absolutely no concept of nail polish only being for girls or reason to think anyone would possibly have a problem with beautiful nails.


But his classmates did have a problem. A big one. Sam was ridiculed for being a boy with nail polish. They called him names and told him to take it off. This lasted the entire day.
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