1. Monitor success rate of a process that may fail
2. Find k closest elements to a value in a sorted Array
3. Quick Sort sorting algorithm in pure immutable Scala
4. Find minimum missing positive number in a sequence
5. Compute a Roman numeral for an Integer, and vice-versa
6. Matching parentheses algorithm with foldLeft and a state machine
7. Traverse a tree Breadth-First, immutably
8. Read a matrix as a spiral
9. Remove duplicates from a sorted list (state machine)
10. Merge Sort: stack-safe, tail-recursive, in pure immutable Scala, N-way
11. Longest increasing sub-sequence length
12. Binary search a generic Array
13. Merge Sort: in pure immutable Scala
14. Is an Array a permutation?
15. Count number of contiguous countries by colors
16. Add numbers without using addition (plus sign)
17. Tic Tac Toe MinMax solve
18. Run-length encoding (RLE) Encoder
19. Print Alphabet Diamond
20. Balanced parentheses algorithm with tail-call recursion optimisation
21. Reverse a String's words efficiently
22. Count number of changes (manipulations) needed to make an anagram with foldLeft and a MultiSet
23. Counting inversions of a sequence (array) using a Merge Sort
24. Check if an array is a palindrome
25. Compute nth row of Pascal's triangle
26. Run-length encoding (RLE) Decoder
27. Check if a number is a palindrome
28. In a range of numbers, count the numbers divisible by a specific integer
29. Reshape a matrix
30. Closest pair of coordinates in a 2D plane
31. Find the contiguous slice with the minimum average
32. Compute maximum sum of subarray (Kadane's algorithm)
33. Rotate Array right in pure-functional Scala - using an unusual immutable efficient approach
34. Length of the longest common substring
35. Tic Tac Toe board check
36. Find an unpaired number in an array
37. Check if a String is a palindrome
38. Count binary gap size of a number using tail recursion
39. Remove duplicates from a sorted list (Sliding)
40. Find sub-array with the maximum sum
41. Find the minimum absolute difference of two partitions
42. Find maximum potential profit from an array of stock price
43. Fibonacci in purely functional immutable Scala
44. Fizz Buzz in purely functional immutable Scala
45. Find combinations adding up to N (non-unique)
46. Count factors/divisors of an integer
47. Compute single-digit sum of digits
48. Traverse a tree Depth-First
49. QuickSelect Selection Algorithm (kth smallest item/order statistic)
50. Rotate a matrix by 90 degrees clockwise

1. Class Inside Class
2. Class Inside Def
3. Collect
4. Def Inside Def
5. Drop, Take, dropRight, takeRight
6. foldLeft and foldRight
7. For-comprehension
8. Lazy List
9. Option Type
10. Ordering
11. Partial Function
12. Pattern Matching
13. Range
14. scanLeft and scanRight
15. Sliding / Sliding Window
16. Stack Safety
17. State machine
18. Tail Recursion
19. Type Class
20. View
21. Zip

How the algorithms look

1. A description/goal of the algorithm.
2. An explanation with both Scala and logical parts.
3. A proof or a derivation, where appropriate.
4. Links to Scala concepts used in this specific algorithm, also unit-tested.
5. An implementation in pure-functional immutable Scala, with efficiency in mind (for most algorithms, this is for paid subscribers only).
6. Unit tests, with a button to run them immediately in our in-browser IDE.