LevenshteinDistance.java

package org.gbif.nub.lookup.similarity;

public class LevenshteinDistance implements StringSimilarity {

  @Override
  public double getSimilarity(String x1, String x2) {
    return DistanceUtils.convertEditDistanceToSimilarity(getDistance(x1, x2), x1, x2);
  }

  public int getDistance (String s0, String s1) {
    int len0 = s0.length() + 1;
    int len1 = s1.length() + 1;

    // the array of distances
    int[] cost = new int[len0];
    int[] newcost = new int[len0];

    // initial cost of skipping prefix in String s0
    for (int i = 0; i < len0; i++) cost[i] = i;

    // dynamically computing the array of distances

    // transformation cost for each letter in s1
    for (int j = 1; j < len1; j++) {
      // initial cost of skipping prefix in String s1
      newcost[0] = j;

      // transformation cost for each letter in s0
      for(int i = 1; i < len0; i++) {
        // matching current letters in both strings
        int match = (s0.charAt(i - 1) == s1.charAt(j - 1)) ? 0 : 1;

        // computing cost for each transformation
        int cost_replace = cost[i - 1] + match;
        int cost_insert  = cost[i] + 1;
        int cost_delete  = newcost[i - 1] + 1;

        // keep minimum cost
        newcost[i] = Math.min(Math.min(cost_insert, cost_delete), cost_replace);
      }

      // swap cost/newcost arrays
      int[] swap = cost; cost = newcost; newcost = swap;
    }

    // the distance is the cost for transforming all letters in both strings
    return cost[len0 - 1];
  }

}