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SergiiVlasiuk's solution

to Spiral Matrix in the Scala Track

Published at Aug 21 2019 · 0 comments
Instructions
Test suite
Solution

Given the size, return a square matrix of numbers in spiral order.

The matrix should be filled with natural numbers, starting from 1 in the top-left corner, increasing in an inward, clockwise spiral order, like these examples:

Spiral matrix of size 3
1 2 3
8 9 4
7 6 5
Spiral matrix of size 4
 1  2  3 4
12 13 14 5
11 16 15 6
10  9  8 7

The Scala exercises assume an SBT project scheme. The exercise solution source should be placed within the exercise directory/src/main/scala. The exercise unit tests can be found within the exercise directory/src/test/scala.

To run the tests simply run the command sbt test in the exercise directory.

For more detailed info about the Scala track see the help page.

Source

Reddit r/dailyprogrammer challenge #320 [Easy] Spiral Ascension. https://www.reddit.com/r/dailyprogrammer/comments/6i60lr/20170619_challenge_320_easy_spiral_ascension/

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

SpiralMatrixTest.scala

import org.scalatest.{Matchers, FunSuite}

/** @version 1.1.0 */
class SpiralMatrixTest extends FunSuite with Matchers {

  test("empty spiral") {
    SpiralMatrix.spiralMatrix(0) should be(List())
  }

  test("trivial spiral") {
    pending
    SpiralMatrix.spiralMatrix(1) should be(List(List(1)))
  }

  test("spiral of size 2") {
    pending
    SpiralMatrix.spiralMatrix(2) should be(List(List(1, 2),
                                                List(4, 3)))
  }

  test("spiral of size 3") {
    pending
    SpiralMatrix.spiralMatrix(3) should be(
      List(List(1, 2, 3), 
           List(8, 9, 4), 
           List(7, 6, 5)))
  }

  test("spiral of size 4") {
    pending
    SpiralMatrix.spiralMatrix(4) should be(
      List(List(1, 2, 3, 4),
           List(12, 13, 14, 5),
           List(11, 16, 15, 6),
           List(10, 9, 8, 7)))
  }

  test("spiral of size 5") {
    pending
    SpiralMatrix.spiralMatrix(5) should be(
      List(List(1, 2, 3, 4, 5),
           List(16, 17, 18, 19, 6),
           List(15, 24, 25, 20, 7),
           List(14, 23, 22, 21, 8),
           List(13, 12, 11, 10, 9)))
  }
}
object SpiralMatrix {
  def spiralMatrix(size: Int): List[List[Int]] = {
    def spiralMatrixValue(size: Int, startValue: Int, row: Int, col: Int): Int = {
      (row, col) match {
        case (0, _) => startValue + col
        case _ if col == size - 1 => startValue + size + row - 1
        case _ if row == size - 1 => startValue + size * 3 - 3 - col
        case (_, 0) => startValue + size * 4 - 4 - row
        case _ => spiralMatrixValue(size - 2, startValue + size * 4 - 4, row - 1, col - 1)
      }
    }
    //    List.range(0, size).map(row =>
    //      List.range(0, size).map(col => spiralMatrixValue(size, 1, row, col)))
    List.tabulate(size, size)((x: Int, y: Int) => spiralMatrixValue(size, 1, x, y))
  }
}

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