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SergiiVlasiuk's solution

to Pascal's Triangle in the Scala Track

Published at Aug 31 2019 · 1 comment
Instructions
Test suite
Solution

Compute Pascal's triangle up to a given number of rows.

In Pascal's Triangle each number is computed by adding the numbers to the right and left of the current position in the previous row.

    1
   1 1
  1 2 1
 1 3 3 1
1 4 6 4 1
# ... etc

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

Pascal's Triangle at Wolfram Math World http://mathworld.wolfram.com/PascalsTriangle.html

Submitting Incomplete Solutions

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

PascalsTriangleTest.scala

import org.scalatest.{Matchers, FunSuite}

/** @version 1.3.0 */
class PascalsTriangleTest extends FunSuite with Matchers {

  test("zero rows") {
    PascalsTriangle.rows(0) should be(List())
  }

  test("single row") {
    pending
    PascalsTriangle.rows(1) should be(List(List(1)))
  }

  test("two rows") {
    pending
    PascalsTriangle.rows(2) should be(List(List(1), List(1, 1)))
  }

  test("three rows") {
    pending
    PascalsTriangle.rows(3) should be(List(List(1), List(1, 1), List(1, 2, 1)))
  }

  test("four rows") {
    pending
    PascalsTriangle.rows(4) should be(
      List(List(1), List(1, 1), List(1, 2, 1), List(1, 3, 3, 1)))
  }

  test("five rows") {
    pending
    PascalsTriangle.rows(5) should be(
      List(List(1),
           List(1, 1),
           List(1, 2, 1),
           List(1, 3, 3, 1),
           List(1, 4, 6, 4, 1)))
  }

  test("six rows") {
    pending
    PascalsTriangle.rows(6) should be(
      List(List(1),
           List(1, 1),
           List(1, 2, 1),
           List(1, 3, 3, 1),
           List(1, 4, 6, 4, 1),
           List(1, 5, 10, 10, 5, 1)))
  }

  test("ten rows") {
    pending
    PascalsTriangle.rows(10) should be(
      List(
        List(1),
        List(1, 1),
        List(1, 2, 1),
        List(1, 3, 3, 1),
        List(1, 4, 6, 4, 1),
        List(1, 5, 10, 10, 5, 1),
        List(1, 6, 15, 20, 15, 6, 1),
        List(1, 7, 21, 35, 35, 21, 7, 1),
        List(1, 8, 28, 56, 70, 56, 28, 8, 1),
        List(1, 9, 36, 84, 126, 126, 84, 36, 9, 1)
      ))
  }

  test("negative rows") {
    pending
    PascalsTriangle.rows(-1) should be(List())
  }
}
object PascalsTriangle {
  private def createPyramide(actualRow: List[Long], nextRow: List[Long]): Stream[List[Long]] = {
    val newRow = nextRow.head :: nextRow.zip(nextRow.tail).map(x => x._1 + x._2) ::: nextRow.last :: Nil
    actualRow #:: createPyramide(nextRow, newRow)
  }

  val pyramid = createPyramide(List(1), List(1, 1))

  def rows(lineNumber: Int): List[List[Long]] = pyramid.take(lineNumber).toList
}

Community comments

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Avatar of SergiiVlasiuk

solution is borrowed from phamduc

What can you learn from this solution?

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