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

Published

## 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:

``````ALGQ
WGRQ
WORQ
SWOD``````

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

## Test cases in Scala

``````assert(
wordInGridDepthFirst(
Array(
Array('A', 'L', 'G', 'Q'),
Array('W', 'G', 'R', 'Q'),
Array('W', 'O', 'R', 'Q'),
Array('S', 'W', 'O', 'D')
),
"ALGO"
)
)
assert(
!wordInGridDepthFirst(
Array(
Array('A', 'L', 'E', 'Q'),
Array('W', 'G', 'R', 'Q'),
Array('W', 'L', 'R', 'Q'),
Array('S', 'W', 'O', 'D')
),
"ALGLE"
)
)
assert(
wordInGridDepthFirst(
Array(
Array('A', 'L', 'E', 'Q'),
Array('W', 'G', 'R', 'Q'),
Array('W', 'L', 'E', 'Q'),
Array('S', 'W', 'O', 'D')
),
"ALGLE"
)
)
``````

## Algorithm in Scala

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

## Explanation

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 www.scala-algorithms.com)

## 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"
surroundInputWith('-')
}

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))
``````

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

## 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.

### Study our 100 Scala Algorithms: 6 fully free, 100 published & 0 upcoming

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

### 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.

## Subscribe to Scala Algorithms

Maximize your Scala with disciplined and consistently unit-tested solutions to 100+ algorithms.

Use it from improving your day-to-day data structures and Scala; all the way to interviewing.