com.github.dylon.liblevenshtein.levenshtein.distance.MemoizedStandard Maven / Gradle / Ivy

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A library for spelling-correction based on Levenshtein Automata.

There is a newer version: 2.2.2

// Generated by delombok at Sat Jul 04 03:49:47 PDT 2015
package com.github.dylon.liblevenshtein.levenshtein.distance;

import com.github.dylon.liblevenshtein.collection.SymmetricImmutablePair;

/**
 * Memoizes the distance between two terms, where the distance is calculated
 * using the standard Levenshtein distance, including the elementary operations
 * of insertion, deletion and substitution.
 * @author Dylon Edwards
 * @since 2.1.0
 */
public class MemoizedStandard extends AbstractMemoized {


  /**
   * {@inheritDoc}
   */
  @Override
  public int memoizedDistance(String v, String w) {
    final com.github.dylon.liblevenshtein.collection.SymmetricImmutablePair key = new SymmetricImmutablePair(v, w);
    int distance = memo.getInt(key);
    if (distance != DEFAULT_RETURN_VALUE) {
      return distance;
    }
    if (v.isEmpty()) {
      distance = w.length();
      memo.put(key, distance);
      return distance;
    }
    if (w.isEmpty()) {
      distance = v.length();
      memo.put(key, distance);
      return distance;
    }
    char a = v.charAt(0);
    String s = v.substring(1);
    char b = w.charAt(0);
    String t = w.substring(1);
    // Discard identical characters
    while (a == b && s.length() > 0 && t.length() > 0) {
      a = s.charAt(0);
      v = s;
      s = v.substring(1);
      b = t.charAt(0);
      w = t;
      t = w.substring(1);
    }
    // s.length() == 0 or t.length() == 0
    if (a == b) {
      distance = s.isEmpty() ? t.length() : s.length();
      memo.put(key, distance);
      return distance;
    }
    distance = memoizedDistance(s, w);
    if (0 == distance) {
      memo.put(key, 1);
      return 1;
    }
    int min_distance = distance;
    distance = memoizedDistance(v, t);
    if (0 == distance) {
      memo.put(key, 1);
      return 1;
    }
    if (distance < min_distance) {
      min_distance = distance;
    }
    distance = memoizedDistance(s, t);
    if (0 == distance) {
      memo.put(key, 1);
      return 1;
    }
    if (distance < min_distance) {
      min_distance = distance;
    }
    distance = 1 + min_distance;
    memo.put(key, distance);
    return distance;
  }
}