Scala algorithm: Print Alphabet Diamond

Published

Algorithm goal

Given a letter such as C, print a diamond using letters A to C, for example:

  A  
 B B 
C   C
 B B 
  A  

Test cases in Scala

assert(fillingLength(forLetter = 'B', toLetter = 'B') == 1)
assert(fillingLength(forLetter = 'B', toLetter = 'C') == 1)
assert(diamond('A') == "A")
assert(diamond('B') == " A \nB B\n A ")
assert(diamond('C') == "  A  \n B B \nC   C\n B B \n  A  ")

Algorithm in Scala

22 lines of Scala (version 2.13), showing how concise Scala can be!

Get the full algorithm Scala algorithms logo, maze part, which looks quirky!

or

'Unlimited Scala Algorithms' gives you access to all the Scala Algorithms!

Upon purchase, you will be able to Register an account to access all the algorithms on multiple devices.

Stripe logo

Explanation

First thing to notice that a Diamond is symmetric vertically: we can then reduce the algorithm to taking the top half, and putting the bottom half by re-using the top through reversing and dropping the last element.

We can in fact represent a range of letters using Scala's Range concept, and from that, compute the length of the padding and the filling around the diamond. (this is © from www.scala-algorithms.com)

Scala provides a simple way to repeat a character multiple times, and String interpolation enables straight-forward concatenation like you would have in languages such as PHP.

Scala concepts & Hints

  1. Drop, Take, dropRight, takeRight

    Scala's `drop` and `take` methods typically remove or select `n` items from a collection.

    assert(List(1, 2, 3).drop(2) == List(3))
    
    assert(List(1, 2, 3).take(2) == List(1, 2))
    
    assert(List(1, 2, 3).dropRight(2) == List(1))
    
    assert(List(1, 2, 3).takeRight(2) == List(2, 3))
    
    assert((1 to 5).take(2) == (1 to 2))
    
  2. Range

    The (1 to n) syntax produces a "Range" which is a representation of a sequence of numbers.

    assert((1 to 5).toString == "Range 1 to 5")
    
    assert((1 to 5).reverse.toString() == "Range 5 to 1 by -1")
    
    assert((1 to 5).toList == List(1, 2, 3, 4, 5))
    
  3. View

    The .view syntax creates a structure that mirrors another structure, until "forced" by an eager operation like .toList, .foreach, .forall, .count.


Scala Algorithms: The most comprehensive library of algorithms in standard pure-functional Scala

Think in Scala & master the highest paid programming language in the US

Scala is used at many places, such as AirBnB, Apple, Bank of America, BBC, Barclays, Capital One, Citibank, Coursera, eBay, JP Morgan, LinkedIn, Morgan Stanley, Netflix, Singapore Exchange, Twitter.

Study our 94 Scala Algorithms: 6 fully free, 54 published & 40 upcoming

Fully unit-tested, with explanations and relevant concepts; new algorithms published about once a week.

  1. Quick Sort sorting algorithm in pure immutable Scala
  2. Find minimum missing positive number in a sequence
  3. Longest increasing sub-sequence length
  4. Counting inversions of a sequence (array) using a Merge Sort
  5. Check if an array is a palindrome
  6. Monitor success rate of a process that may fail
  7. Find combinations adding up to N (non-unique)
  8. Find combinations adding up to N (unique)
  9. Find k closest elements to a value in a sorted Array
  10. Compute a Roman numeral for an Integer, and vice-versa
  11. Matching parentheses algorithm with foldLeft and a state machine
  12. Traverse a tree Breadth-First, immutably
  13. Read a matrix as a spiral
  14. Remove duplicates from a sorted list (state machine)
  15. Merge Sort: stack-safe, tail-recursive, in pure immutable Scala, N-way
  16. Binary search a generic Array
  17. Merge Sort: in pure immutable Scala
  18. Is an Array a permutation?
  19. Count number of contiguous countries by colors
  20. Add numbers without using addition (plus sign)
  21. Tic Tac Toe MinMax solve
  22. Run-length encoding (RLE) Encoder
  23. Print Alphabet Diamond
  24. Balanced parentheses algorithm with tail-call recursion optimisation
  25. Reverse a String's words efficiently
  26. Count number of changes (manipulations) needed to make an anagram with foldLeft and a MultiSet
  27. Compute nth row of Pascal's triangle
  28. Run-length encoding (RLE) Decoder
  29. Check if a number is a palindrome
  30. In a range of numbers, count the numbers divisible by a specific integer
  31. Find the index of a substring ('indexOf')
  32. Reshape a matrix
  33. Closest pair of coordinates in a 2D plane
  34. Find the contiguous slice with the minimum average
  35. Compute maximum sum of subarray (Kadane's algorithm)
  36. Binary search in a rotated sorted array
  37. Rotate Array right in pure-functional Scala - using an unusual immutable efficient approach
  38. Length of the longest common substring
  39. Tic Tac Toe board check
  40. Find an unpaired number in an array
  41. Check if a String is a palindrome
  42. Count binary gap size of a number using tail recursion
  43. Remove duplicates from a sorted list (Sliding)
  44. Find sub-array with the maximum sum
  45. Find the minimum absolute difference of two partitions
  46. Find maximum potential profit from an array of stock price
  47. Fibonacci in purely functional immutable Scala
  48. Fizz Buzz in purely functional immutable Scala
  49. Count factors/divisors of an integer
  50. Compute single-digit sum of digits
  51. Traverse a tree Depth-First
  52. Reverse bits of an integer
  53. QuickSelect Selection Algorithm (kth smallest item/order statistic)
  54. Rotate a matrix by 90 degrees clockwise

Explore the 21 most useful Scala concepts

To save you going through various tutorials, we cherry-picked the most useful Scala concepts in a consistent form.

  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

Register now (free)