| #1 | Balanced parentheses algorithm with tail-call recursion optimisationBalanced parentheses algorithm with tail-call recursion | Free |
| #2 | Check if an array is a palindromeCheck if an array is a palindrome | Free |
| #3 | Find an unpaired number in an arrayFind an unpaired number in an array | Free |
| #4 | Count binary gap size of a number using tail recursionCount binary gap size of a number using tail recursion | Free |
| #5 | Find maximum potential profit from an array of stock priceFind maximum potential profit from an array of stock price | Free |
| #6 | Fizz Buzz in purely functional immutable ScalaFizz Buzz in purely functional immutable Scala | Free |
| #7 | Binary heap (min-heap)Binary heap (min-heap) | Solution: US$3.99Free test cases & hints |
| #8 | Compute missing rangesCompute missing ranges | Solution: US$3.99Free test cases & hints |
| #9 | Find kth largest element in a ListFind kth largest element in a List | Solution: US$3.99Free test cases & hints |
| #10 | Find the minimum item in a rotated sorted arrayFind the minimum item in a rotated sorted array | Solution: US$3.99Free test cases & hints |
| #11 | Compute the steps to transform an anagram only using swapsCompute the steps to transform an anagram only using swaps | Solution: US$3.99Free test cases & hints |
| #12 | Compute minimum number of Fibonacci numbers to reach sumCompute minimum number of Fibonacci numbers to reach sum | Solution: US$3.99Free test cases & hints |
| #13 | Fixed Window Rate LimiterFixed Window Rate Limiter | Solution: US$3.99Free test cases & hints |
| #14 | Token Bucket Rate LimiterToken Bucket Rate Limiter | Solution: US$3.99Free test cases & hints |
| #15 | Leaky Bucket Rate LimiterLeaky Bucket Rate Limiter | Solution: US$3.99Free test cases & hints |
| #16 | Least-recently used cache (MRU)Least-recently used cache (MRU) | Solution: US$3.99Free test cases & hints |
| #17 | Game of LifeGame of Life | Solution: US$3.99Free test cases & hints |
| #18 | Find triplets that sum to a target ('3Sum')Find triplets that sum to a target ('3Sum') | Solution: US$3.99Free test cases & hints |
| #19 | Reverse Polish Notation calculatorReverse Polish Notation calculator | Solution: US$3.99Free test cases & hints |
| #20 | Mars RoverMars Rover | Solution: US$3.99Free test cases & hints |
| #21 | Find indices of tuples that sum to a target (Two Sum)Find indices of tuples that sum to a target (Two Sum) | Solution: US$3.99Free test cases & hints |
| #22 | Sliding Window Rate LimiterSliding Window Rate Limiter | Solution: US$3.99Free test cases & hints |
| #23 | Compute modulo of an exponent without exponentiationCompute modulo of an exponent without exponentiation | Solution: US$3.99Free test cases & hints |
| #24 | Count pairs of a given expected sumCount pairs of a given expected sum | Solution: US$3.99Free test cases & hints |
| #25 | Establish execution order from dependenciesEstablish execution order from dependencies | Solution: US$3.99Free test cases & hints |
| #26 | Check a binary tree is balancedCheck a binary tree is balanced | Solution: US$3.99Free test cases & hints |
| #27 | Compute keypad possibilitiesCompute keypad possibilities | Solution: US$3.99Free test cases & hints |
| #28 | Reverse first n elements of a queueReverse first n elements of a queue | Solution: US$3.99Free test cases & hints |
| #29 | Least-recently used cache (LRU)Least-recently used cache (LRU) | Solution: US$3.99Free test cases & hints |
| #30 | Find height of binary treeFind height of binary tree | Solution: US$3.99Free test cases & hints |
| #31 | Check a binary tree is a search treeCheck a binary tree is a search tree | Solution: US$3.99Free test cases & hints |
| #32 | Make a binary search tree (Red-Black tree)Make a binary search tree (Red-Black tree) | Solution: US$3.99Free test cases & hints |
| #33 | Check a directed graph has a routing between two nodes (depth-first search)Check a directed graph has a routing between two nodes | Solution: US$3.99Free test cases & hints |
| #34 | Longest common prefix of stringsLongest common prefix of strings | Solution: US$3.99Free test cases & hints |
| #35 | Check if a directed graph has cyclesCheck if a directed graph has cycles | Solution: US$3.99Free test cases & hints |
| #36 | Pure-functional double linked listPure-functional double linked list | Solution: US$3.99Free test cases & hints |
| #37 | Count passing carsCount passing cars | Solution: US$3.99Free test cases & hints |
| #38 | Remove duplicates from an unsorted ListRemove duplicates from an unsorted List | Solution: US$3.99Free test cases & hints |
| #39 | Make a queue using MapsMake a queue using Maps | Solution: US$3.99Free test cases & hints |
| #40 | Make a queue using stacks (Lists in Scala)Make a queue using stacks (Lists in Scala) | Solution: US$3.99Free test cases & hints |
| #41 | Single-elimination tournament treeSingle-elimination tournament tree | Solution: US$3.99Free test cases & hints |
| #42 | Compute the length of longest valid parenthesesCompute the length of longest valid parentheses | Solution: US$3.99Free test cases & hints |
| #43 | Binary search in a rotated sorted arrayBinary search in a rotated sorted array | Solution: US$3.99Free test cases & hints |
| #44 | Find combinations adding up to N (unique)Find combinations adding up to N (unique) | Solution: US$3.99Free test cases & hints |
| #45 | Find the index of a substring ('indexOf')Find the index of a substring ('indexOf') | Solution: US$3.99Free test cases & hints |
| #46 | Reverse bits of an integerReverse bits of an integer | Solution: US$3.99Free test cases & hints |
| #47 | Find k closest elements to a value in a sorted ArrayFind k closest elements to a value in a sorted Array | Solution: US$3.99Free test cases & hints |
| #48 | Reshape a matrixReshape a matrix | Solution: US$3.99Free test cases & hints |
| #49 | Remove duplicates from a sorted list (Sliding)Remove duplicates from a sorted list (Sliding) | Solution: US$3.99Free test cases & hints |
| #50 | Remove duplicates from a sorted list (state machine)Remove duplicates from a sorted list (state machine) | Solution: US$3.99Free test cases & hints |
| #51 | Find combinations adding up to N (non-unique)Find combinations adding up to N (non-unique) | Solution: US$3.99Free test cases & hints |
| #52 | Compute single-digit sum of digitsCompute single-digit sum of digits | Solution: US$3.99Free test cases & hints |
| #53 | Add numbers without using addition (plus sign)Add numbers without using addition (plus sign) | Solution: US$3.99Free test cases & hints |
| #54 | Tic Tac Toe MinMax solveTic Tac Toe MinMax solve | Solution: US$3.99Free test cases & hints |
| #55 | Compute nth row of Pascal's triangleCompute nth row of Pascal's triangle | Solution: US$3.99Free test cases & hints |
| #56 | Print Alphabet DiamondPrint Alphabet Diamond | Solution: US$3.99Free test cases & hints |
| #57 | Reverse a String's words efficientlyReverse a String's words efficiently | Solution: US$3.99Free test cases & hints |
| #58 | Monitor success rate of a process that may failMonitor success rate of a process that may fail | Solution: US$3.99Free test cases & hints |
| #59 | QuickSelect Selection Algorithm (kth smallest item/order statistic)QuickSelect Selection Algorithm | Solution: US$3.99Free test cases & hints |
| #60 | Rotate a matrix by 90 degrees clockwiseRotate a matrix by 90 degrees | Solution: US$3.99Free test cases & hints |
| #61 | Read a matrix as a spiralRead a matrix as a spiral | Solution: US$3.99Free test cases & hints |
| #62 | Count number of contiguous countries by colorsCount number of contiguous countries by colors | Solution: US$3.99Free test cases & hints |
| #63 | Length of the longest common substringLength of the longest common substring | Solution: US$3.99Free test cases & hints |
| #64 | Find minimum missing positive number in a sequenceFind minimum missing positive number in a sequence | Solution: US$3.99Free test cases & hints |
| #65 | Binary search a generic ArrayBinary search a generic Array | Solution: US$3.99Free test cases & hints |
| #66 | Run-length encoding (RLE) DecoderRun-length encoding (RLE) Decoder | Solution: US$3.99Free test cases & hints |
| #67 | Run-length encoding (RLE) EncoderRun-length encoding (RLE) Encoder | Solution: US$3.99Free test cases & hints |
| #68 | Find the contiguous slice with the minimum averageFind the contiguous slice with the minimum average | Solution: US$3.99Free test cases & hints |
| #69 | Tic Tac Toe board checkTic Tac Toe board check | Solution: US$3.99Free test cases & hints |
| #70 | Find the minimum absolute difference of two partitionsFind the minimum absolute difference of two partitions | Solution: US$3.99Free test cases & hints |
| #71 | Compute a Roman numeral for an Integer, and vice-versaCompute a Roman numeral for an Integer, and vice-versa | Solution: US$3.99Free test cases & hints |
| #72 | Quick Sort sorting algorithm in pure immutable ScalaQuick Sort sorting algorithm in pure immutable Scala | Solution: US$3.99Free test cases & hints |
| #73 | Fibonacci in purely functional immutable ScalaFibonacci in purely functional immutable Scala | Solution: US$3.99Free test cases & hints |
| #74 | In a range of numbers, count the numbers divisible by a specific integerCount numbers divisible by another | Solution: US$3.99Free test cases & hints |
| #75 | Is an Array a permutation?Is an array a permutation? | Solution: US$3.99Free test cases & hints |
| #76 | Merge Sort: stack-safe, tail-recursive, in pure immutable Scala, N-wayMerge Sort: stack-safe, tail-recursive | Solution: US$3.99Free test cases & hints |
| #77 | Closest pair of coordinates in a 2D planeClosest pair of coordinates in a 2D plane | Solution: US$3.99Free test cases & hints |
| #78 | Counting inversions of a sequence (array) using a Merge SortCounting inversions of a sequence | Solution: US$3.99Free test cases & hints |
| #79 | Rotate Array right in pure-functional Scala - using an unusual immutable efficient approachRotate Array right in pure-functional Scala | Solution: US$3.99Free test cases & hints |
| #80 | Count factors/divisors of an integerCount factors of a number | Solution: US$3.99Free test cases & hints |
| #81 | Merge Sort: in pure immutable ScalaMerge Sort: in pure immutable Scala | Solution: US$3.99Free test cases & hints |
| #82 | Longest increasing sub-sequence lengthLongest increasing sub-sequence length | Solution: US$3.99Free test cases & hints |
| #83 | Matching parentheses algorithm with foldLeft and a state machineMatching parentheses algorithm with a state machine | Solution: US$3.99Free test cases & hints |
| #84 | Traverse a tree Breadth-First, immutablyTraverse a tree Breadth-First, immutably | Solution: US$3.99Free test cases & hints |
| #85 | Count number of changes (manipulations) needed to make an anagram with an efficient foldLeftCount number of changes for making an anagram | Solution: US$3.99Free test cases & hints |
| #86 | Check if a number is a palindromeCheck if a number is a palindrome | Solution: US$3.99Free test cases & hints |
| #87 | Compute maximum sum of subarray (Kadane's algorithm)Compute maximum sum of subarray (Kadane's algorithm) | Solution: US$3.99Free test cases & hints |
| #88 | Check if a String is a palindromeCheck if a String is a palindrome | Solution: US$3.99Free test cases & hints |
| #89 | Find sub-array with the maximum sumFind sub-array with the maximum sum | Solution: US$3.99Free test cases & hints |
| #90 | Traverse a tree Depth-FirstTraverse a tree Depth-First | Solution: US$3.99Free test cases & hints |
| #91 | Maximum wait at a fuel stationMaximum wait at a fuel station | Available 5th April |
| #92 | Count dist intersectionsCount dist intersections | Available 20th April |
| #93 | Print a binary treePrint a binary tree | Available 8th May |
| #94 | Find the longest palindrome within a stringFind the longest palindrome within a string | Available 20th May |
| #95 | Median of two sorted arraysMedian of two sorted arrays | Available 8th June |
| #96 | Check word in grid (depth-first search)Check word in grid (depth-first search) | Available 20th June |
| #97 | Check word in grid (stack-safe)Check word in grid (stack-safe) | Available 8th July |
| #98 | Merge intervalsMerge intervals | Available 20th July |
| #99 | Check Sudoku boardCheck Sudoku board | Available 8th August |
| #100 | Print a binary tree verticallyPrint a binary tree vertically | Available 20th August |