1. Monitor success rate of a process that may fail
2. Find combinations adding up to N (unique)
3. Find k closest elements to a value in a sorted Array
4. Quick Sort sorting algorithm in pure immutable Scala
5. Find minimum missing positive number in a sequence
6. Compute a Roman numeral for an Integer, and vice-versa
7. Matching parentheses algorithm with foldLeft and a state machine
8. Traverse a tree Breadth-First, immutably
9. Read a matrix as a spiral
10. Remove duplicates from a sorted list (state machine)
11. Merge Sort: stack-safe, tail-recursive, in pure immutable Scala, N-way
12. Longest increasing sub-sequence length
13. Binary search a generic Array
14. Merge Sort: in pure immutable Scala
15. Is an Array a permutation?
16. Count number of contiguous countries by colors
17. Add numbers without using addition (plus sign)
18. Tic Tac Toe MinMax solve
19. Run-length encoding (RLE) Encoder
20. Print Alphabet Diamond
21. Balanced parentheses algorithm with tail-call recursion optimisation
22. Reverse a String's words efficiently
23. Count number of changes (manipulations) needed to make an anagram with foldLeft and a MultiSet
24. Counting inversions of a sequence (array) using a Merge Sort
25. Check if an array is a palindrome
26. Compute nth row of Pascal's triangle
27. Run-length encoding (RLE) Decoder
28. Check if a number is a palindrome
29. In a range of numbers, count the numbers divisible by a specific integer
30. Find the index of a substring ('indexOf')
31. Reshape a matrix
32. Closest pair of coordinates in a 2D plane
33. Find the contiguous slice with the minimum average
34. Compute maximum sum of subarray (Kadane's algorithm)
35. Binary search in a rotated sorted array
36. Rotate Array right in pure-functional Scala - using an unusual immutable efficient approach
37. Length of the longest common substring
38. Tic Tac Toe board check
39. Find an unpaired number in an array
40. Check if a String is a palindrome
41. Count binary gap size of a number using tail recursion
42. Remove duplicates from a sorted list (Sliding)
43. Find sub-array with the maximum sum
44. Find the minimum absolute difference of two partitions
45. Find maximum potential profit from an array of stock price
46. Fibonacci in purely functional immutable Scala
47. Fizz Buzz in purely functional immutable Scala
48. Find combinations adding up to N (non-unique)
49. Count factors/divisors of an integer
50. Compute single-digit sum of digits
51. Traverse a tree Depth-First
52. Reverse bits of an integer
53. QuickSelect Selection Algorithm (kth smallest item/order statistic)
54. 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.