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Finding the Levenshtein Distance in Scala

Posted on April 24, 2008, in Programming

In the spirit of esoteric code snippets like this one, I thought I’d put my two bob in :)

I have written the Levenshtein Distance algorithm using Scala below. The Levensthein Distance algorithm is a Dynamic Programming Algorithm (DPA). This implementation is a little different to the Python one (which creates the arrays explicitly and fills them using loops):

import scalaz.memo.Memo
import scalaz.memo.SizedMemo.arraySizedMemo

object Levenshtein {
  def levenshtein[A](x: Array[A], y: Array[A]): Int = {
    val im = arraySizedMemo
    val m = im[Memo[Int, Int]](x.length + 1)
    // the call matrix
    def mx(i: Int, j: Int): Int = if(i == 0) j else if(j == 0) i else {
      def f = (n: Int) => im[Int](y.length + 1)
      val a = m(f)(i - 1)(mx(i - 1, _))(j) + 1
      val b = m(f)(i - 1)(mx(i - 1, _))(j - 1) + (if(x(i - 1) == y(j - 1)) 0 else 1)
      lazy val c = m(f)(i)(mx(i, _))(j - 1) + 1
      if(a < b) a else if(b <= c) b else c
    }
    mx(x.length, y.length)
  }

  def main(args: Array[String]) =
    println(levenshtein(args(0).toCharArray, args(1).toCharArray))
}

To run this code:

$ wget http://projects.workingmouse.com/public/scalaz/artifacts/2.4/scalaz.jar # download Scalaz 2.4
$ scalac -classpath scalaz.jar Levenshtein.scala # compile
$ scala -classpath .:scalaz.jar Levenshtein algorithm altruistic # find the distance!
<strong>6</strong>