1. Compute the length of longest valid parentheses
2. Monitor success rate of a process that may fail
3. Find combinations adding up to N (unique)
4. Find k closest elements to a value in a sorted Array
5. Make a queue using stacks (Lists in Scala)
6. Single-elimination tournament tree
7. Quick Sort sorting algorithm in pure immutable Scala
8. Find minimum missing positive number in a sequence
9. Compute a Roman numeral for an Integer, and vice-versa
10. Matching parentheses algorithm with foldLeft and a state machine
11. Traverse a tree Breadth-First, immutably
12. Read a matrix as a spiral
13. Remove duplicates from a sorted list (state machine)
14. Merge Sort: stack-safe, tail-recursive, in pure immutable Scala, N-way
15. Longest increasing sub-sequence length
16. Binary search a generic Array
17. Merge Sort: in pure immutable Scala
18. Make a queue using Maps
19. Is an Array a permutation?
20. Count number of contiguous countries by colors
21. Add numbers without using addition (plus sign)
22. Tic Tac Toe MinMax solve
23. Run-length encoding (RLE) Encoder
24. Print Alphabet Diamond
25. Balanced parentheses algorithm with tail-call recursion optimisation
26. Reverse a String's words efficiently
27. Count number of changes (manipulations) needed to make an anagram with foldLeft and a MultiSet
28. Counting inversions of a sequence (array) using a Merge Sort
29. Check if an array is a palindrome
30. Compute nth row of Pascal's triangle
31. Run-length encoding (RLE) Decoder
32. Check if a number is a palindrome
33. In a range of numbers, count the numbers divisible by a specific integer
34. Find the index of a substring ('indexOf')
35. Reshape a matrix
36. Closest pair of coordinates in a 2D plane
37. Find the contiguous slice with the minimum average
38. Compute maximum sum of subarray (Kadane's algorithm)
39. Binary search in a rotated sorted array
40. Rotate Array right in pure-functional Scala - using an unusual immutable efficient approach
41. Length of the longest common substring
42. Tic Tac Toe board check
43. Find an unpaired number in an array
44. Check if a String is a palindrome
45. Count binary gap size of a number using tail recursion
46. Remove duplicates from a sorted list (Sliding)
47. Find sub-array with the maximum sum
48. Find the minimum absolute difference of two partitions
49. Find maximum potential profit from an array of stock price
50. Fibonacci in purely functional immutable Scala
51. Fizz Buzz in purely functional immutable Scala
52. Find combinations adding up to N (non-unique)
53. Remove duplicates from an unsorted List
54. Count factors/divisors of an integer
55. Compute single-digit sum of digits
56. Traverse a tree Depth-First
57. Reverse bits of an integer
58. QuickSelect Selection Algorithm (kth smallest item/order statistic)
59. 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.