Day(1): Looking for a CS Job!

Hello, i have been employed by the world’s worst boss for 3 months, but i decided to finally break free and call it quits.

i have been unemployed for 16 days, which is not a lot if you think about it, but i am a young adult and i can worry and have anxiety as much as i like god damn it!

I love medium so much, like i really fucking do. i even pay the monthly subscription; (5$ is like 100 of my currency, so yeah!).

so i decided to daily sum what i did, so i can have a better understanding and a log of what i did and eventually look back (please soon?) and appreciate the effort i did.

So Here is what i did Today:

Read Chapter (5) In Grokking Algorithms about Hash tables and Hash Functions and other Article about hashing!

Honestly, i was always worried that i didn’t understand them correctly, but turns out i already do, but i needed a refresher when collision happens, and the idea of having a linked list totally skipped my mind! so yeah i learned that today.

and i read this amazing article (Breaking Down: SHA-1 Algorithm. Looking under the hood and… | by Aditya Anand | InfoSec Write-ups | Medium) which explains SHA-1 Algorithm.

the cool thing about SHA is that they are locally insensitive, which means changing a letter from Dog to Dug for example, yields two different complete results! fucking cool. (there is a variant called SimHash which is uncool, yeah you guessed it right, locally sensitive.. but i guess you can check similar items with it if you are boring).

Shootout to Proff. Hazem from AinShams (he taught me a lot about RSA , Diffie-Hellman algorithms: Public/Private keys)

i did some simple problem solving about hashing too:
Encode and Decode TinyURL — LeetCode (it’s basically intended so you can make a Hash function with a corresponding hash table or just a map with an index if you want, how am i to judge) For this question, i decided i would just for every string, i would return a prime number and that’s it, and while this is simple solution, i thought about the obvious limitation of extra long big numbers, that will require me to generate large prime numbers every iteration (which is a complex problem in computational number theory: Generation of primes — Wikipedia), so instead of generating a prime number, let’s modulo by a prime number! (lecture2.pdf (ox.ac.uk))

Problem Solving a day , keeps sleeping mind away

i fucking love python, let’s just make that clear too.

but you know who doesn’t like python, people who interview me, i am waiting for the upcoming interview of mine (monday woohoo!) and it’s for a C++ position, so to break the mold of me always using python ,i will try and solve today’s December challenge using C++ ( i will even use auto, don’t judge me)

it was called 4SUM II, and for my luck, it was also tagged with Hashing.

it took me more than i care to admit, but i did it.

you are given 4 Vectors: A B C D and you are required to find tubles (i,j,k,l) that will A[i}+…+D[L]=0.

I made a map with A+B and map with -(C+D). and viola, it’s over.

Computer Vision is … Visionary!

i have been working with making a project where you use your hand to draw something (hand is detected by either segmentation or SSD Net) and then the drawing takes place.

i am achieving good results: https://youtu.be/O0KwbtfEN0w (This is from yesterday) but i wanted to try a SSD (Single shot detection) and i ended up using Google’s Mediapipe (Although it’s incredibly noisey at some test cases).

so i guess i have to figure a way to use both of them at the same time.

Also, i read few pages of the contour section from the Learning OpenCV3 book. (it’s a cool book, but amazingly lacking in maths), i am trying to brain storm to find a way to be able to get only one point per corner.

i want to basically get one Yellow point per ‘corner’. i did some conditioning which works -most- of the cases, will try to improve it and work in parrallel with mediapipe’s solution.

So Today’s progress is :

1- Tried to Use GoodFeaturesToTrack and HarrisCornerDetection in an attempt to filter those points, but it didn’t work out.

2- Approximating the Hull (red) to a poly didn’t yield good results.

3- Tried Fine tuning the filteration but results didn’t make much of a difference.

4- Added the ability to draw when using mediapipe.

(i may come back later on this blogpost and update if i though of something else)

Pointers that are ..SMART?

i learned today about std::unique_ptr,std::shared_ptr and std::weak_ptr.

in Brief, they are called smart pointers because you don’t manually delete them and you don’t use the ‘new’ keyword with them.

Unique_ptr cannot be copied, hence it’s unique hehe.

SharedPtr can be copied, and when it’s copied, a control block alled Ref_Counter increases. and that underlying entity is deleted when that Ref_Counter Reaches Zero.

WeakPtr is a version of SharedPtr that can copy from the sharedPtr, but doesn’t increase the count.

to create a sharedPtr use make_shared and obv. to create a Unique pointer, you guessed it.. i know you did … make_unique()

fucking cool.

so yeah.. i learned that from the Cherno on youtube.

Machine Learning Explainability On kaggle

Permutation Importance : After the model is fit on the data, shuffle one column (One feature) and see how much our prediction goes wrong due to the shuffling of that feature

Partial plots: Slightly Changing a feature on one-axis, plot the difference in the prediction. (If we it’s a regression model of course)

Feature Importance: Golden feature, the feature that has the most weight on determining the output.

SHAP: breaks down a prediction to show the impact of each feature.

Polymorphism!

Read this amazing article on medium:

Everything You Need to Know About Polymorphism | by Drew Campbell | Better Programming | Medium

Take away is about the Cons of Polymorphism: All you need to know for our purposes is that polymorphic behaviour is enabled in C++ using something called a virtual table. A virtual table is an array that stores the addresses of all the virtual functions for a class. When a call is made on a virtual function, the code must navigate to the virtual table, look up which function to call, then go to the address and call to the function. With a normal non-virtual function, we simply go to the function’s address. In certain situations where the computer is already doing a lot of work, these extra steps can slow things down.

Problem solving!

Did few more and that’s the end!

Solving the questions found in this excel sheet!

60 LeetCode problems to solve for coding interiew — Google Sheets