programming progress

Wednesday, June 07, 2017

Running React Native Packager and Android Emulator on a Different Port

React Native Packager and the Android Emulator uses port 8081 by default. To use a different port (let's say 8082):

1. Add "--port=8082" to the react-native start command, like this:

react-native start --port=8082

2. With your application open in the Android Emulator (and has an error because it can't read from port 8081), trigger the developer menu using the following on the command line:

adb shell input keyevent 82

3. Navigate to Dev Settings > Debug server host & port for device, and enter your host and port, use this Stackoverflow comment as guide: https://stackoverflow.com/questions/37900078/react-native-could-not-connect-to-development-server/38117960#38117960

Wednesday, March 23, 2016

Common PowerMock and EasyMock Use Cases and Properties

Hand-rolled Mocks

They're Fast

EasyMock

Use when a Hand-rolled mock will be very large and/or cumbersome
If you do not need any PowerMock features

PowerMock

Hard to trace using debugger
If you need assumptions about the internal code that cannot be reached by EasyMock
For testing with statics and singletons
For testing difficult to mock classes like java.io.File
For accessing private fields
For suppressing methods

Monday, March 23, 2015

Algorithms Books and Online Judges Tandems

Here are some of them:

1. UVa Online Judge + Skiena/Revilla, Halim

2. ACM-ICPC Live Archive + Revilla/Poucher

3. Rosalind Algorithmic Heights + Dasgupta/Papadimitriou

4. Rosalind Bioinformatics + Compeau/Pevzner

5. Programming Challenges + Skiena/Revilla

6. Codility + Codility

They do have their own learning materials.

Thursday, March 19, 2015

Academic Online Judges

Wednesday, March 18, 2015

Codingame Puzzles

Single Player: 51

Tutorial
1. Onboarding -> finding a minimal value

Easy
1. Power of Thor -> condition statements (if...).
2. The Descent -> search in an array
3. Skynet: the Chasm -> conditional statements (if...)
4. Mars Lander - Level 1 -> Speed regulation.
5. Temperatures -> search in an array.
6. ASCII Art -> proper storage and retrieval in an array.
7. Chuck Norris -> encoding/decoding.
8. MIME Type -> maps, string parsing.
9. Defibrillators -> Distance calculation, Big data.
10. Horse-racing Duals -> sorting, finding a minimum.

Medium
1. Skynet: the Virus -> search in a graph.
2. Heat Detector -> Convergence.
3. Teads Sponsored Challenge -> Graph theory
4. Winamax Sponsored Challenge -> String manipulation
5. Mars Lander - Level 2 -> Position, speed and angle regulation.
6. The Paranoid Android -> greedy algorithm.
7. Indiana - Level 1 -> maps.
8. Stock Exchange Losses -> Search through a set of values. Dynamic Programming
9. Network Cabling -> Optimal distance.
10. Conway Sequence -> Conway sequence.
11. Telephone Numbers -> storage optimization. Tries
12. Dwarfs standing on the shoulder of giants -> Tree traversal.
13. Bender, a depressed robot -> Trajectory Calculation.
14. Scrabble -> Weighting.
15. The Gift -> Distribution.
16. Mayan Calculation -> Algebraic calculations.
17. APU - Init Phase -> Searching in a list

Hard
1. The Labyrinth -> Pathfinding, optimization.
2. Skynet strikes back -> Tree search and traversal.
3. The Paranoid Android - One step further -> pathfinding and optimisation.
4. Skynet: The Bridge -> Depth-first search or Backtracking
5. Indiana - Level 2 -> Pathfinding.
6. Vox Codei -> Brute-force.
7. Thor VS Giants -> Centroid computation.
8. Super Computer -> Scheduling.
9. Roller Coaster -> Calculation.
10. CGX Formatter -> Text formatting.
11. TAN Network -> Pathfinding in a graph.
12. Genome Sequencing -> Pattern recognition. Permutations
13. Surface -> Grid flooding.
14. Bender - The Money Machine -> Weighted Pathfinding
15. Bender - Algorithmic Complexity -> Complexity calculation.
16. APU - Improvement Phase -> Backtracking, Pruning, Brute-forcing

Very Hard
1. Nintendo Sponsored Challenge -> C++
2. Triangulation -> Triangulation.
3. The Resistance -> Decyphering.
4. Indiana - Level 3 -> Pathfinding in a grid.
5. Vox Codei - Redux -> brute-force, exploration.
6. Music Scores -> Image (as bit array) processing.
7. Mars Lander - Level 3 -> Position, speed and angle regulation.

Multiplayer
1. Tron Battle
2. Game of Drones
3. Poker Chip Race
4. Poker Chip Race
5. Platinum Rift
6. Platinum Rift 2
7. The Great Escape

Monday, January 19, 2015

Steve Yegge - Get that job at Google - Short Summary

Data Structures and Algorithms

- Algorithm Complexity/Big-O
- Sorting: Mergesort/Quicksort
- Hashtables
- Trees: binary trees, n-ary trees, tries, Red-Black/AVL/splay tree
- Traversal: BFS, DFS, inorder, preorder, postorder
- Graphs: objects-pointers/adjacency-list/matrix representation, traversal
- Dijkstra, A*
- NP-completeness, traveling salesman, knapsack

Others

- Discrete Math
- OS: processes, threads, concurrency, locks, mutexes, semaphores, monitors, deadlock, livelock, context switching, scheduling
- bring your own dry-erase marker

Friday, December 12, 2014

Codility Lessons - Slides

Updated: Jul. 22, 2016

1. Iterations

Tasks: 1/1

for loop, while loop, looping over a collection

2. Arrays

Tasks: 1/2

array operations, reversing an array

3. Time Complexity

Tasks: 3/3

dominant operation, space complexity, arithmetic sequence/progression, arithmetic series: n(n+1)/2

4. Counting Elements

Tasks: 4/4

swapped elements in identical lists

5. Prefix Sums

Tasks: 2/4

6. Sorting

Tasks: 3/4

7. Stacks and Queues

Tasks: 2/4

8. Leader

Tasks: 2/2

Boyer-Moore Majority algorithm

9. Maximum Slice Problem

Tasks: 3/3

Kadane's algorithms for negative and non-negative elements, Maximum profit, wrong approaches: two pointers, etc.

10. Prime and Composite Numbers

Tasks: 2/4

If i is a divisor of n, n/i is also a divisor. 1 is neither prime nor composite.

11. Sieve of Eratosthenes

Tasks: 1/2

Semiprimes (product of two primes, bonus: prefix sums)

12. Euclidean GCD Algorithm

Tasks: 1/2

Original GCD algorithm by Euclid: Recursively subtract the smaller number from the larger. GCD by subtraction, GCD by Division, LCM.

13. Fibonacci Numbers

Tasks: 2

14. Binary Search

Tasks: 2

15. Caterpillar Method

Tasks: 4

16. Greedy Algorithms

Tasks: 2

17. Dynamic Programming

Tasks: 2

18. Indeed Prime 2015 challenge

Tasks: 3

19. Indeed Prime 2016 challenge

Tasks: 4

20. Indeed Prime 2016 College Coders challenge

Tasks: 1/4

19. Future training

Tasks: 5

Total Tasks: 63

Wednesday, November 19, 2014

Learn Programming Languages and Technologies Interactively Online

Python
http://www.codecademy.com/tracks/python
http://www.learnpython.org
http://www.pyschools.com
http://interactivepython.org
http://pythonmonk.com
https://www.hackerrank.com/domains/miscellaneous/python-tutorials
http://www.pythonchallenge.com
http://codecombat.com
http://www.checkio.org
http://www.trypython.org

R
http://tryr.codeschool.com
https://www.datacamp.com

React
https://www.freecodecamp.com

React Native
https://facebook.github.io/react-native
http://www.reactnativeexpress.com

Regex
https://regexcrossword.com
https://www.hackerrank.com/domains/regex/re-introduction

Ruby
http://www.codecademy.com/tracks/ruby
https://rubymonk.com
https://www.codeschool.com
http://www.learn-ruby.org

Scala
https://www.scala-exercises.org
http://www.scala-tour.com/
http://scalatutorials.com/

Talentbuddy Problems

Updated: June 15, 2015

Total: 136
Normal: 50
Medium: 56
Hard: 30

Normal

Average grade

Binary

Binary float

Bottle

Bounce rate

Caesar shift

Common courses

Copy-Paste

Count digits

Count occurences

Count ones

Count substrings

Count tokens

Count words
Countries
Find character

Find substring

FizzBuzz

Float division

Growth

Highest grade

Integer division

Invert sum

Linear equation

Max

Mean

Merge Sort

Missing number

Odd square sum

Pair product

Pair Sum

Prediction

Prime numbers
Request counting

Remove stop words
Remove substring
Scheduling
Select substring

Simple sum
Sorting Students

Sort names

Sort words

Sorting students

Standard deviation

Student progress

Successful students

Time

Top locations

Vowel count

Z-score

Medium

2^n
Arithmetic evaluation
AST Part One
Bacon number
Balanced brackets
Basic search query
Book store
Brands
Compute average
Copy async
Currency exchange
Depth first traversal
Dispatcher
Divide by 2
Even number
Find String
Fraction
Heads and tails
Indexes
Intersecting street segments
Linked List Cycle
Longest improvement
Longest palindrome
Longest street segment
Majority number
Max sum
Median
Medical app
Multiply by 2
Neighbourhood
Nth number
Nth permutation
PACO
Parallel async
Plane tickets
Power of 2
Precision
Priority
Purchase tracking
Query tokens stemming
Rain
Read async
Relative sort
Selection
Semantic analysis
Set bit
Shopping cart
Skyscrapers
Sorted merge
Speed
Swap values
Tokenize query
Topological sort
Unset bit
User administration
User table

Hard

AST Part Two
Check
Chocolate bars
Coins
Contact management
Context extraction
Context pruning
Extract book titles
Failure detection
Fast power
Hash String
Intermediary code
LLVM parser
Map matcher
Mapper
Palindromes count
Pouring
Price experiment
Pub crawl
Reducer
Selection
Simple expression
Social network
Sqrt
Streets nearby
Trigger words
Tuple sum
Tweets per second
Typeahead
Unique sequence

Number of Talentbuddy Practice Problems in Groups

Updated: March 8, 2015

Languages - 34

Getting Started - 2
Web Analytics - 5
Classroom Analysis - 7
Text Editor - 5
Data Conversion - 6
Simple Loops - 6
Expressions - 3

Tech Interviews - 52

Elementary Data Structures - 7
Sorting and Order Statistics - 6
Search - 5
Elementary Graph Problems - 9
Advanced Techniques - 3
Math - 7
General Interview Practice - 5
HubSpot Challenges - 2
Redbeacon Challenges - 2
Twitter Challenges - 2
Uber Challenges - 4

Databases - 11

MongoDB Basics - 7
Redis Basics - 4

Projects - 24

Search Engine - 4
Books - 4
Map Reduce - 4
GPS Positioning - 5
Sysmbolic Execution - 7

Fun - 141

Tokenize Query - Lessons - 4
Bounce Rate - Lessons - 3
Computer Vision - Lessons - 3
Programming Basics - 6
Expressions - 3
Simple Loops - 6
Data Conversion - 6
Search - 5
Advanced Techniques - 3
Twitter Challenges - 2
Text Editor - 5
Search Engine - 4
MongoDB Basics - 7
Redis Basics - 4
Elementary Graph Problems - 9
Google Interview - 4
Simple Interview - 2
HubSpot Challenges - 2
Uber Challenges - 4
Web Analytics - 5
Classroom Analysis - 7
Books - 4
GPS Positioning - 5
Map Reduce - 4
Symbolic Execution - 7
Getting Started - 2
Elementary Data Structures - 7
Sorting and Order Statistics - 6
Math - 7
General Interview Practice - 5
Redbeacon Challenges - 2
Async JavaScript - 3

Monday, November 17, 2014

Runner Runner - Surprising Life Lessons

It's dangerous to work for gambling-related businesses. I assume most, if not all, people there are psychopaths. (How about public a.k.a. share-price-driven companies? Most companies?)

Been offered to work for one before, turned it down to protect my religious reputation. Turns out, protecting this reputation protects my life, too. Reputation is everything, says one of the 48 Laws of Power.

Someone I know worked for a company whose client is a casino. Also had psychopaths of their own. Or there are just a lot of psychopaths at the top?

Sunday, November 02, 2014

7. CodeChef
8. Brilliant
9. InterviewBit
10. Codewars
11. Codingame
12. Codility
13. Topcoder
14. Project Euler
15. CodeFights
16. CodingBat
17. SPOJ
18. CoderByte
19. LintCode
20. UVA Online Judge

21. CheckiO
22. Kattis
23. SQL-EX.RU
24. PythonChallenge
25. CodeAbbey
26. Rosalind
27. CodeKata
28. CSAcademy
29. CrowdANALYTIX
30. Elements of Programming Interviews Judge
31. CodeStepByStep

32. TunedIT

33. FightCode
34. HPC University

35. CodeEval

36. MLComp
37. ChallengePost
38. BeatMyCode
39. Talentbuddy

Notable Others:
- Google Code Jam
- Facebook Hacker Cup

NOTES:
- Most are based on the Online Judge system
- TopCoder, CrowdANALYTIX, Kaggle, ChallengePost and TunedIT have their focus on Data Science/Projects
- Codingame and FightCode have their focus on game playing programs, so this includes intelligent solutions, Machine Learning, AI
- MLComp is focused on Machine Learning
- Rosalind is focused on Bioinformatics
- SQL-EX.RU is the only one in the list focusing on SQL. HackerRank added SQL, too.
- HPC University is focused on High Performance Computing (HPC)
- CheckiO is focused on Python
- Most on the list, especially the commercial ones are pitching employment, just keep this in mind
- HackerEarth, CodeEval, Talentbuddy, Codility, and Kattis are focused on Employment, have about 400 (practice), 185, 120, 90, and 600 problems respectively
- GeeksforGeeks Practice, LeetCode and LintCode are focused on Tech Interview Problems, (have about ?, 180 and 160 problems, respectively). LeetCode also has some SQL problems.
- HackerRank includes other specialties from the other sites like AI (Codingame), Data Science (TopCoder, Kaggle), Python Tutorials (CheckiO), Eulerian Problems (Project Euler).
- HackerRank provides a good calendar that contains events from other sites like HackerEarth, CodeChef, URI Online Judge, TopCoder, CodeForces
- HackerRank-only features: Functional Programming specialization, Bash specialization, Linux Text utilities specialization
- Brilliant.org is more on High School Mathematics, and also are not a competition site, but they have problems in Computer Science, too.
- PythonChallenge is a programming riddles site and is actually not limited to Python

Looking for Academic Online Judges?

Monday, October 27, 2014

NoSQL Companies Glassdoor Technical Interviews

DataStax (Cassandra)

1) Describe some challenges of provisioning software across a datacenter consisting of thousands of nodes

2) How would you go about programming the Kevin Bacon problem?

Couchbase

1) In databases, what is the difference between a delete statement and a truncate statement?

MongoDB

1) How would you design an online chat system with separate room

2) The input array was sorted integers, how to square all the elements and keep it sorted?

3) Taking in two strings, find out if they are anagrams

4) Find the largest prime divisor of a number

5) Given a string of parantheses, brackets, and curly braces, write a function that returns whether the string is well balanced, in that every left delimiter is closed by the correct right delimiter

6) Print the prime factors of the input number

7) How various search algorithm O time change if done in parallel on multi cpu machine

8) How many gas stations in the United States?

9) How would you write DB write / access functions to make sure data is not modified by threads.

10) Parse mathematical expression given as chars in array ['1', '+', '2,' '/', '4']

11) Write algorithm to find loop in graph. The graph is unidirectional with any number of connections. The graph is not necessarily connected

12) Write code to convert integer to string.

13) Fizzbuzz

14) Find the height of a binary tree

15) Parsing parenthesis. Given a set of open and close parenthesis, make sure the string is valid, such that each open parenthesis has a matching close parenthesis in the correct place

16) We have a person who logs into a website using their Facebook credentials. Anything they post to that website can be seen by their friends and those friends' friends only.

17) Name several different sorting algorithms and rank them by their computational complexity.

18) Write an algorithm that tells if 2 and only two numbers in a 1x3 array are the same.

19) Given a word, how to find all anagrams in a dictionary.

20) Reverse a linked list

21) How much water is on the planet (earth)?

Cloudera (Hadoop)

1) Design gmail from the ground up

2) Write a function to do the "Exponentiation" . i.e power(a,b) where a is raised to b. Eg: power(3,2) gives 9. power(5,2) gives 25 etc

3) Find the common elements in two arrays

4) Grid search algorithm and analyzing its time complexity, and then various alternative implementations that would minimize data storage or the order of the algorithm.

5) Given an m*n matrix with all its elments=1. Also given a list of (x,y) points. The question was to make the elements of xth row and yth column as zero. Optimise it.

6) Array Pair sum, provide O(N) solution

7) Recursive Permutation

8) Implement few methods of a Linked-list (like append, getAtIndex, removeAtIndex, size)

9) Find the total number of 1s in a byte array

10) Generate a random 4 letter word from /usr/share/dict/words

11) 1TB of data on my laptop --> sort the data

12) Distributed Merge Sort algorithm

13) A file contains a billion integers, try to find any one integer that is not in the file.

14) How would you find two numbers that add to a sum in an array?

15) How would you find three numbers that add to a sum in an array?

16) How would you implement hash table on your own? Write the code for implementing your own hash table?

17) If you wanted to make a highly concurrent cache with a least recently used replacement policy, what data structures would you use? How would this scale per number of threads?

Hortonworks (Hadoop)

1) Word sorting in a file

2) Binary search

3) Implement file system using class

4) Implement hashmap

MapR (Hadoop)

1) Implement a hash table

2) Determining if a tree is a valid binary tree

3) Write a recursive algorithm( return true if there is a path from root to a leaf with total sum == sum)

4) LRU Cache

5) There are numbers from 1..n in a list of numbers with size (n+k) with k duplicates. Print k duplicates.

6) Read from a huge file say 1tb and write it into a huge file and scale it

7) BFS, insert line breaks after every level (not necessarily balanced)

8) Clock angle question

Basho (Riak)

AeroSpike

Tuesday, April 16, 2013

Easyrec recommendation engine

... and others like it. Might be useful someday, somehow..

Tuesday, April 09, 2013

HashSet, TreeSet equivalent in Linux

I was thinking of implementing a command line version of Java HashSet, LinkedHashSet and TreeSet when I remembered sort and uniq.

Just use uniq as you would a HashSet/LinkedHashSet. And sort a you would a TreeSet. And use GnuWin32 on Windows.

Goodbye new open-source project. Perhaps a command line version of Map, SortedMap, and BidiMap?

Update (April 10, 2013): There is still hope for Set.retainAll() (union), Set.removeAll() (intersection)..

Saturday, March 09, 2013

New technology weekend!

Node.js, Redis, MongoDB, Mashery I/O Docs, Google Apps Script...

Thursday, February 21, 2013

Java Enterprise Architecture Requirements: S.P.A.M.M.E.R.S

Section 2 (Common Architectures) of Java EE 5 Enterprise Architect Certified Master Exam has this: Explain the advantages and disadvantages of two-tier/three-tier/multi-tier architectures when examined under the following topics: scalability, maintainability, reliability, availability, extensibility, performance, manageability, and security. That's a lot of architectural requirements and the initial acronym is SMRAEPMS, which does't look easy to remember. Rearranging, we have:

S - scalability
P - performance
A - availability
M - maintainability
M - manageability
E - extensibility
R - reliability
S - security

Here's some spam:

Wednesday, February 13, 2013

My Java Development Tools for a New Computer

- Dropbox
- putty, pageant, puttygen
- winscp
- MySQL
- MySQL Workbench
- Java
- Eclipse
- Google Talk
- Skype

Editors:
- notepad++
- textpad
- HxD
Grep:
- dnGrep
- Windows Grep
Diff:
- Diffmerge - main
- Winmerge
- KDiff3
Zip:
- Winrar
- Winzip
- 7zip
Others:
- GnuWin32
- Chrome/Safari/Opera/Firefox
- Free Download Manager
- Filezilla FTP Client
- RealVNC
- Antivirus

When to use multithreading?

Based on my experiences:

1) When multiple tasks need to be running at the same time.

We created a mobile game where we have individual threads for the music, the graphics update, and for reading the input.

2) When it is beneficial for tasks to be running at the same time.

I needed to communicate with a web service that returns a very large amount of information. There is also a limit to the amount of information that it returns. This can be done serially, requesting chunks of information at a time. Multiple requests can also be done at the same time, so I opted for multithreading, significantly reducing the amount of time to retrieve all the needed information.

Monday, February 11, 2013

SimpleDateFormat in Java is not Thread-Safe, Use Carefully

http://stackoverflow.com/questions/4021151/java-dateformat-is-not-threadsafe-what-does-this-leads-to