Scala algorithm: Check word in grid (depth-first search)


Algorithm goal

Determine whether a specified word exists contiguously a grid. The rules are: letters cannot be re-used, you can only go left, right, up, or down. For example, 'ALGO' is a word in the following grid:


There is the same problem but with a stack-safe Stack Safetysolution, at: CheckWordInGridStackSafe

Test cases in Scala

      Array('A', 'L', 'G', 'Q'),
      Array('W', 'G', 'R', 'Q'),
      Array('W', 'O', 'R', 'Q'),
      Array('S', 'W', 'O', 'D')
      Array('A', 'L', 'E', 'Q'),
      Array('W', 'G', 'R', 'Q'),
      Array('W', 'L', 'R', 'Q'),
      Array('S', 'W', 'O', 'D')
      Array('A', 'L', 'E', 'Q'),
      Array('W', 'G', 'R', 'Q'),
      Array('W', 'L', 'E', 'Q'),
      Array('S', 'W', 'O', 'D')

Algorithm in Scala

31 lines of Scala (compatible versions 2.13 & 3.0), showing how concise Scala can be!

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For each index in the grid, we generate a point, and then during the downward traversal, we include points we have already seen in a separate Set. This allows us to not touch points we already have touched.

For a more stack-safe solution, see: CheckWordInGridStackSafe (Stack Safety). (this is © from

Scala concepts & Hints

  1. Def Inside Def

    A great aspect of Scala is being able to declare functions inside functions, making it possible to reduce repetition.

    def exampleDef(input: String): String = {
      def surroundInputWith(char: Char): String = s"$char$input$char"
    assert(exampleDef("test") == "-test-")

    It is also frequently used in combination with Tail Recursion.

  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))

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  6. Find height of binary tree
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  10. Check word in grid (depth-first search)
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  13. Least-recently used cache (LRU)
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Explore the 22 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. Variance
  21. View
  22. Zip

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