Finding how many times a given string is a substring of another string using scala

Question

what is the elegant way for finding how many times a given string is a substring of another string using scala?

The below test cases that should make clear what are the requirements:

import org.scalatest.FunSuite

class WordOccurrencesSolverTest extends FunSuite {

  private val solver = new WordOccurrencesSolver()

  test("solve for a in a") {
    assert(solver.solve("a", "a") === 1)
  }

  test("solve for b in a") {
    assert(solver.solve("b", "a") === 0)
  }

  test("solve for a in aa") {
    assert(solver.solve("a", "aa") === 2)
  }

  test("solve for b in ab") {
    assert(solver.solve("b", "ab") === 1)
  }

  test("solve for ab in ab") {
    assert(solver.solve("ab", "ab") === 1)
  }

  test("solve for ab in abab") {
    assert(solver.solve("ab", "abab") === 2)
  }

  test("solve for aa in aaa") {
    assert(solver.solve("aa", "aaa") === 2)
  }
}

Here is my solution to the problem of which I am not particularly proud:

class WordOccurrencesSolver {

  def solve(word: String, text: String): Int = {
    val n = word.length
    def solve(acc: Int, word: String, sb: String): Int = sb match {
      case _ if sb.length < n => acc
      case _ if sb.substring(0, n) == word => solve(acc + 1, word, sb.tail)
      case _ => solve(acc, word, sb.tail)
    }
    solve(0, word, text)
  }

}

I assume there must be a clean one liner which takes advantage of Scala's higher order functions instead of recursion and match/case clause.

Answer 1

If you are looking for an idiomatic Scala solution then you can use the sliding to create a sliding window iterator and count the wondows which are equal to your target String.

This solution while being functional also offers you an acceptable performence.

def countOccurrences(src: String, tgt: String): Int =
  src.sliding(tgt.length).count(window => window == tgt)

Answer 2

You can probably use this java function:

StringUtils.countMatches(stringToFindMatchesIn, keyWordToFind );

This will return the number of occurences of the keyword in the string