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/**
* Copyright (C) 2006-2014 phloc systems
* http://www.phloc.com
* office[at]phloc[dot]com
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.phloc.commons.text.utils;
import javax.annotation.Nonnegative;
import javax.annotation.Nonnull;
import javax.annotation.Nullable;
import javax.annotation.concurrent.Immutable;
import com.phloc.commons.ValueEnforcer;
import com.phloc.commons.annotations.PresentForCodeCoverage;
import com.phloc.commons.string.StringHelper;
/**
* Utility class for calculating the Levenshtein distance of 2 strings.
*
* @author Philip Helger
*/
@Immutable
public final class LevenshteinDistance
{
@PresentForCodeCoverage
@SuppressWarnings ("unused")
private static final LevenshteinDistance s_aInstance = new LevenshteinDistance ();
private LevenshteinDistance ()
{}
/**
* Main generic Levenshtein implementation that uses "1" for all costs!
*
* @param aStr1
* Not null
* @param nLen1
* > 0
* @param aStr2
* Not null
* @param nLen2
* > 0
* @return non negative distance
*/
private static int _getDistance111 (@Nonnull final char [] aStr1,
@Nonnegative final int nLen1,
@Nonnull final char [] aStr2,
@Nonnegative final int nLen2)
{
// previous cost array, horizontally
int [] aPrevRow = new int [nLen1 + 1];
// cost array, horizontally
int [] aCurRow = new int [nLen1 + 1];
// temp vars
int i, j, nSubstVal;
int ch2;
int [] tmp;
// init
for (i = 0; i <= nLen1; i++)
aPrevRow[i] = i;
for (j = 0; j < nLen2; j++)
{
ch2 = aStr2[j];
aCurRow[0] = j + 1;
for (i = 0; i < nLen1; i++)
{
nSubstVal = aStr1[i] == ch2 ? 0 : 1;
aCurRow[i + 1] = Math.min (Math.min (aCurRow[i] + 1, aPrevRow[i + 1] + 1), aPrevRow[i] + nSubstVal);
}
// swap current distance counts to 'previous row' distance counts
tmp = aPrevRow;
aPrevRow = aCurRow;
aCurRow = tmp;
}
// our last action in the above loop was to switch d and p, so p now
// actually has the most recent cost counts
return aPrevRow[nLen1];
}
/**
* Main generic Levenshtein implementation. Assume all preconditions are
* checked.
*
* @param aStr1
* Not null
* @param nLen1
* > 0
* @param aStr2
* Not null
* @param nLen2
* > 0
* @param nCostInsert
* ≥ 0
* @param nCostDelete
* ≥ 0
* @param nCostSubstitution
* ≥ 0
* @return non negative distance
*/
private static int _getDistance (@Nonnull final char [] aStr1,
@Nonnegative final int nLen1,
@Nonnull final char [] aStr2,
@Nonnegative final int nLen2,
@Nonnegative final int nCostInsert,
@Nonnegative final int nCostDelete,
@Nonnegative final int nCostSubstitution)
{
// previous cost array, horizontally
int [] aPrevRow = new int [nLen1 + 1];
// cost array, horizontally
int [] aCurRow = new int [nLen1 + 1];
// temp vars
int i, j, ch2, nSubstCost;
int [] tmp;
// init
for (i = 0; i <= nLen1; i++)
aPrevRow[i] = i * nCostInsert;
for (j = 0; j < nLen2; j++)
{
ch2 = aStr2[j];
aCurRow[0] = (j + 1) * nCostDelete;
for (i = 0; i < nLen1; i++)
{
nSubstCost = aStr1[i] == ch2 ? 0 : nCostSubstitution;
aCurRow[i + 1] = Math.min (Math.min (aCurRow[i] + nCostInsert, aPrevRow[i + 1] + nCostDelete), aPrevRow[i] +
nSubstCost);
}
// swap current distance counts to 'previous row' distance counts
tmp = aPrevRow;
aPrevRow = aCurRow;
aCurRow = tmp;
}
// our last action in the above loop was to switch d and p, so p now
// actually has the most recent cost counts
return aPrevRow[nLen1];
}
/**
* Get the distance of the 2 strings, using the costs 1 for insertion,
* deletion and substitution.
*
* @param aStr1
* First string.
* @param aStr2
* Second string.
* @return The Levenshtein distance.
*/
public static int getDistance (@Nullable final char [] aStr1, @Nullable final char [] aStr2)
{
final int nLen1 = aStr1 == null ? 0 : aStr1.length;
final int nLen2 = aStr2 == null ? 0 : aStr2.length;
if (nLen1 == 0)
return nLen2;
if (nLen2 == 0)
return nLen1;
return _getDistance111 (aStr1, nLen1, aStr2, nLen2);
}
public static int getDistance (@Nullable final char [] aStr1,
@Nullable final char [] aStr2,
@Nonnegative final int nCostInsert,
@Nonnegative final int nCostDelete,
@Nonnegative final int nCostSubstitution)
{
ValueEnforcer.isGE0 (nCostInsert, "InsertionCost");
ValueEnforcer.isGE0 (nCostDelete, "DeletionCost");
ValueEnforcer.isGE0 (nCostSubstitution, "SubstitutionCost");
final int nLen1 = aStr1 == null ? 0 : aStr1.length;
final int nLen2 = aStr2 == null ? 0 : aStr2.length;
if (nLen1 == 0)
return nLen2 * nCostInsert;
if (nLen2 == 0)
return nLen1 * nCostInsert;
// Fallback to more efficient variant?
if (nCostInsert == 1 && nCostDelete == 1 && nCostSubstitution == 1)
return _getDistance111 (aStr1, nLen1, aStr2, nLen2);
return _getDistance (aStr1, nLen1, aStr2, nLen2, nCostInsert, nCostDelete, nCostSubstitution);
}
/**
* Get the distance of the 2 strings, using the costs 1 for insertion,
* deletion and substitution.
*
* @param sStr1
* First string.
* @param sStr2
* second string.
* @return The Levenshtein distance.
*/
public static int getDistance (@Nullable final String sStr1, @Nullable final String sStr2)
{
final int nLen1 = StringHelper.getLength (sStr1);
final int nLen2 = StringHelper.getLength (sStr2);
if (nLen1 == 0)
return nLen2;
if (nLen2 == 0)
return nLen1;
return _getDistance111 (sStr1.toCharArray (), nLen1, sStr2.toCharArray (), nLen2);
}
public static int getDistance (@Nullable final String sStr1,
@Nullable final String sStr2,
@Nonnegative final int nCostInsert,
@Nonnegative final int nCostDelete,
@Nonnegative final int nCostSubstitution)
{
ValueEnforcer.isGE0 (nCostInsert, "InsertionCost");
ValueEnforcer.isGE0 (nCostDelete, "DeletionCost");
ValueEnforcer.isGE0 (nCostSubstitution, "SubstitutionCost");
final int nLen1 = StringHelper.getLength (sStr1);
final int nLen2 = StringHelper.getLength (sStr2);
if (nLen1 == 0)
return nLen2 * nCostInsert;
if (nLen2 == 0)
return nLen1 * nCostInsert;
// Fallback to more efficient variant?
if (nCostInsert == 1 && nCostDelete == 1 && nCostSubstitution == 1)
return _getDistance111 (sStr1.toCharArray (), nLen1, sStr2.toCharArray (), nLen2);
return _getDistance (sStr1.toCharArray (),
nLen1,
sStr2.toCharArray (),
nLen2,
nCostInsert,
nCostDelete,
nCostSubstitution);
}
}
