How our 100 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.

1. Compute the length of longest valid parentheses
2. Check a binary tree is balanced
3. Print a binary tree
4. Remove duplicates from an unsorted List
5. Make a queue using stacks (Lists in Scala)
6. Find height of binary tree
7. Single-elimination tournament tree
8. Reverse Polish Notation calculator
9. Quick Sort sorting algorithm in pure immutable Scala
10. Maximum wait at a fuel station
11. Find minimum missing positive number in a sequence
12. Least-recently used cache (LRU)
13. Count pairs of a given expected sum
14. Binary heap (min-heap)
15. Compute a Roman numeral for an Integer, and vice-versa
16. Compute keypad possibilities
17. Matching parentheses algorithm with foldLeft and a state machine
18. Traverse a tree Breadth-First, immutably
19. Read a matrix as a spiral
20. Remove duplicates from a sorted list (state machine)
21. Token Bucket Rate Limiter
22. Leaky Bucket Rate Limiter
23. Merge Sort: stack-safe, tail-recursive, in pure immutable Scala, N-way
24. Longest increasing sub-sequence length
25. Reverse first n elements of a queue
26. Binary search a generic Array
27. Game of Life
28. Merge Sort: in pure immutable Scala
29. Make a queue using Maps
30. Is an Array a permutation?
31. Count number of contiguous countries by colors
32. Add numbers without using addition (plus sign)
33. Tic Tac Toe MinMax solve
34. Run-length encoding (RLE) Encoder
35. Print Alphabet Diamond
36. Find kth largest element in a List
37. Balanced parentheses algorithm with tail-call recursion optimisation
38. Reverse a String's words efficiently
39. Count number of changes (manipulations) needed to make an anagram with an efficient foldLeft
40. Count passing cars
41. Count dist intersections
42. Establish execution order from dependencies
43. Counting inversions of a sequence (array) using a Merge Sort
44. Longest common prefix of strings
45. Check if an array is a palindrome
46. Compute missing ranges
47. Check a directed graph has a routing between two nodes (depth-first search)
48. Compute nth row of Pascal's triangle
49. Run-length encoding (RLE) Decoder
50. Check if a number is a palindrome
51. In a range of numbers, count the numbers divisible by a specific integer
52. Compute minimum number of Fibonacci numbers to reach sum
53. Find the longest palindrome within a string
54. Find the index of a substring ('indexOf')
55. Reshape a matrix
56. Compute the steps to transform an anagram only using swaps
57. Compute modulo of an exponent without exponentiation
58. Closest pair of coordinates in a 2D plane
59. Find the contiguous slice with the minimum average
60. Compute maximum sum of subarray (Kadane's algorithm)
61. Pure-functional double linked list
62. Binary search in a rotated sorted array
63. Check if a directed graph has cycles
64. Rotate Array right in pure-functional Scala - using an unusual immutable efficient approach
65. Check a binary tree is a search tree
66. Length of the longest common substring
67. Sliding Window Rate Limiter
68. Tic Tac Toe board check
69. Find an unpaired number in an array
70. Check if a String is a palindrome
71. Count binary gap size of a number using tail recursion
72. Remove duplicates from a sorted list (Sliding)
73. Monitor success rate of a process that may fail
74. Least-recently used cache (MRU)
75. Find sub-array with the maximum sum
76. Find the minimum absolute difference of two partitions
77. Find maximum potential profit from an array of stock price
78. Fibonacci in purely functional immutable Scala
79. Fizz Buzz in purely functional immutable Scala
80. Find triplets that sum to a target ('3Sum')
81. Find combinations adding up to N (non-unique)
82. Find the minimum item in a rotated sorted array
83. Make a binary search tree (Red-Black tree)
84. Mars Rover
85. Find combinations adding up to N (unique)
86. Find indices of tuples that sum to a target (Two Sum)
87. Count factors/divisors of an integer
88. Compute single-digit sum of digits
89. Fixed Window Rate Limiter
90. Traverse a tree Depth-First
91. Reverse bits of an integer
92. Find k closest elements to a value in a sorted Array
93. QuickSelect Selection Algorithm (kth smallest item/order statistic)
94. 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