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