| #1 | Balanced parentheses algorithm with tail-call recursion optimisationBalanced parentheses algorithm with tail-call recursion optimisation | 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 | Compute single-digit sum of digitsCompute single-digit sum of digits | Solution: US$1.99Free test cases & hints |
| #8 | Add numbers without using addition (plus sign)Add numbers without using addition (plus sign) | Solution: US$1.99Free test cases & hints |
| #9 | Tic Tac Toe MinMax solveTic Tac Toe MinMax solve | Solution: US$1.99Free test cases & hints |
| #10 | Compute nth row of Pascal's triangleCompute nth row of Pascal's triangle | Solution: US$1.99Free test cases & hints |
| #11 | Print Alphabet DiamondPrint Alphabet Diamond | Solution: US$1.99Free test cases & hints |
| #12 | Reverse a String's words efficientlyReverse a String's words efficiently | Solution: US$1.99Free test cases & hints |
| #13 | Monitor success rate of a process that may failMonitor success rate of a process that may fail | Solution: US$1.99Free test cases & hints |
| #14 | QuickSelect Selection Algorithm (kth smallest item/kth order statistic)QuickSelect Selection Algorithm (kth smallest item/kth order statistic) | Solution: US$1.99Free test cases & hints |
| #15 | Rotate a matrix by 90 degrees clockwiseRotate a matrix by 90 degrees | Solution: US$1.99Free test cases & hints |
| #16 | Read a matrix as a spiralRead a matrix as a spiral | Solution: US$1.99Free test cases & hints |
| #17 | Count number of contiguous countries by colorsCount number of contiguous countries by colors | Solution: US$1.99Free test cases & hints |
| #18 | Length of the longest common substringLength of the longest common substring | Solution: US$1.99Free test cases & hints |
| #19 | Find minimum missing positive number in a sequenceFind minimum missing positive number in a sequence | Solution: US$1.99Free test cases & hints |
| #20 | Binary search a generic ArrayBinary search a generic Array | Solution: US$1.99Free test cases & hints |
| #21 | Run-length encoding (RLE) DecoderRun-length encoding (RLE) Decoder | Solution: US$1.99Free test cases & hints |
| #22 | Run-length encoding (RLE) EncoderRun-length encoding (RLE) Encoder | Solution: US$1.99Free test cases & hints |
| #23 | Find the contiguous slice with the minimum averageFind the contiguous slice with the minimum average | Solution: US$1.99Free test cases & hints |
| #24 | Tic Tac Toe board checkTic Tac Toe board check | Solution: US$1.99Free test cases & hints |
| #25 | Find the minimum absolute difference of two partitionsFind the minimum absolute difference of two partitions | Solution: US$1.99Free test cases & hints |
| #26 | Compute a Roman numeral for an Integer, and vice-versaCompute a Roman numeral for an Integer, and vice-versa | Solution: US$1.99Free test cases & hints |
| #27 | Quick Sort sorting algorithm in pure immutable ScalaQuick Sort sorting algorithm in pure immutable Scala | Solution: US$1.99Free test cases & hints |
| #28 | Fibonacci in purely functional immutable ScalaFibonacci in purely functional immutable Scala | Solution: US$1.99Free test cases & hints |
| #29 | In a range of numbers, count the numbers divisible by a specific integerCount numbers divisible by another | Solution: US$1.99Free test cases & hints |
| #30 | Is an Array a permutation?Is an array a permutation? | Solution: US$1.99Free test cases & hints |
| #31 | Merge Sort: stack-safe, tail-recursive, in pure immutable Scala, N-wayMerge Sort: stack-safe, tail-recursive | Solution: US$1.99Free test cases & hints |
| #32 | Closest pair of coordinates in a 2D planeClosest pair of coordinates in a 2D plane | Solution: US$1.99Free test cases & hints |
| #33 | Counting inversions of a sequence (array) using a Merge SortCounting inversions of a sequence | Solution: US$1.99Free test cases & hints |
| #34 | Rotate Array right in pure-functional Scala - using an unusual immutable efficient approachRotate Array right in pure-functional Scala | Solution: US$1.99Free test cases & hints |
| #35 | Count factors/divisors of an integerCount factors of a number | Solution: US$1.99Free test cases & hints |
| #36 | Merge Sort: in pure immutable ScalaMerge Sort: in pure immutable Scala | Solution: US$1.99Free test cases & hints |
| #37 | Longest increasing sub-sequence lengthLongest increasing sub-sequence length | Solution: US$1.99Free test cases & hints |
| #38 | Matching parentheses algorithm with foldLeft and a state machineMatching parentheses algorithm with foldLeft and a state machine | Solution: US$1.99Free test cases & hints |
| #39 | Traverse a tree Breadth-First, immutablyTraverse a tree Breadth-First, immutably | Solution: US$1.99Free test cases & hints |
| #40 | Count number of changes (manipulations) needed to make an anagram with foldLeft and a MultiSetCount number of changes for making an anagram | Solution: US$1.99Free test cases & hints |
| #41 | Check if a number is a palindromeCheck if a number is a palindrome | Solution: US$1.99Free test cases & hints |
| #42 | Compute maximum sum of subarray (Kadane's algorithm)Compute maximum sum of subarray (Kadane's algorithm) | Solution: US$1.99Free test cases & hints |
| #43 | Check if a String is a palindromeCheck if a String is a palindrome | Solution: US$1.99Free test cases & hints |
| #44 | Find sub-array with the maximum sumFind sub-array with the maximum sum | Solution: US$1.99Free test cases & hints |
| #45 | Traverse a tree Depth-FirstTraverse a tree Depth-First | Solution: US$1.99Free test cases & hints |
| #46 | Find combinations adding up to NFind combinations adding up to N | Available 13th March |
| #47 | Remove duplicates from a sorted list (state machine)Remove duplicates from a sorted list (state machine) | Available 20th March |
| #48 | Remove duplicates from a sorted list (Sliding)Remove duplicates from a sorted list (Sliding) | Available 27th March |
| #49 | Reshape a matrixReshape a matrix | Available 3rd April |
| #50 | Find k closest elements to a value in a sorted ArrayFind k closest elements to a value in a sorted Array | Available 10th April |
| #51 | Reverse bits of an integerReverse bits of an integer | Available 17th April |
| #52 | Find the index of a substring ('indexOf')Find the index of a substring ('indexOf') | Available 24th April |
| #53 | Binary search in a rotated sorted arrayBinary search in a rotated sorted array | Available 30th April |
| #54 | Compute the length of longest valid parenthesesCompute the length of longest valid parentheses | Available 1st May |
| #55 | Single-elimination tournament treeSingle-elimination tournament tree | Available 8th May |
| #56 | Make a queue using stacks (Lists in Scala)Make a queue using stacks (Lists in Scala) | Available 15th May |
| #57 | Make a queue using MapsMake a queue using Maps | Available 15th May |
| #58 | Remove duplicates from an unsorted listRemove duplicates from an unsorted list | Available 22nd May |
| #59 | Count passing carsCount passing cars | Available 29th May |
| #60 | Pure-functional double linked listPure-functional double linked list | Available 29th May |
| #61 | Check if a directed graph has cyclesCheck if a directed graph has cycles | Available 5th June |
| #62 | Longest common prefix of stringsLongest common prefix of strings | Available 12th June |
| #63 | Check a directed graph has a routing between two nodes (depth-first search)Check a directed graph has a routing between two nodes (depth-first search) | Available 28th June |
| #64 | Make a binary search treeMake a binary search tree | Available 5th July |
| #65 | Check a binary tree is a search treeCheck a binary tree is a search tree | Available 12th July |
| #66 | Find height of binary treeFind height of binary tree | Available 19th July |
| #67 | Least-recently used cache (LRU)Least-recently used cache (LRU) | Available 26th July |
| #68 | Reverse first n elements of a queueReverse first n elements of a queue | Available 2nd August |
| #69 | Compute keypad possibilitiesCompute keypad possibilities | Available 9th August |
| #70 | Check a binary tree is balancedCheck a binary tree is balanced | Available 16th August |
| #71 | Establish execution order from dependenciesEstablish execution order from dependencies | Available 23rd August |
| #72 | Count pairs of a given expected sumCount pairs of a given expected sum | Available 30th August |
| #73 | Compute modulo of an exponent without exponentiationCompute modulo of an exponent without exponentiation | Available 6th September |
| #74 | Binary heapBinary heap | Available 13th September |
| #75 | Compute the steps to transform an anagram only using swapsCompute the steps to transform an anagram only using swaps | Available 13th September |
| #76 | Binomial heapBinomial heap | Available 20th September |
| #77 | Game of LifeGame of Life | Available 28th September |
