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[COLLECTIONS-456] Added ListUtils.longestCommonSubsequence(List, List). 

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/collections/trunk@1477312 13f79535-47bb-0310-9956-ffa450edef68
This commit is contained in:
Thomas Neidhart 2013-04-29 20:08:46 +00:00
parent 72f33c83d4
commit 969ffdbb98
3 changed files with 96 additions and 1 deletions
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5
src/changes/changes.xml
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@ -22,6 +22,9 @@
<body> <body>
<release version="4.0" date="TBA" description="Next release"> <release version="4.0" date="TBA" description="Next release">
<action issue="COLLECTIONS-456" dev="tn" type="add">
Added method "ListUtils#longestCommonSubsequence(List, List)".
</action>
<action issue="COLLECTIONS-454" dev="tn" type="update"> <action issue="COLLECTIONS-454" dev="tn" type="update">
An iterator over a "Flat3Map#entrySet()" will now return An iterator over a "Flat3Map#entrySet()" will now return
independent Map.Entry objects that will not change anymore when independent Map.Entry objects that will not change anymore when
@ -135,7 +138,7 @@
</action> </action>
<action issue="COLLECTIONS-404" dev="luc" type="add" due-to="Jordane Sarda"> <action issue="COLLECTIONS-404" dev="luc" type="add" due-to="Jordane Sarda">
Added an implementation of Eugene Myers difference algorithm in package Added an implementation of Eugene Myers difference algorithm in package
o.a.c.c.comparators.sequence. o.a.c.c.sequence.
</action> </action>
<action issue="COLLECTIONS-400" dev="tn" type="fix" due-to="Shin Hwei Tan"> <action issue="COLLECTIONS-400" dev="tn" type="fix" due-to="Shin Hwei Tan">
Added missing null check in "CollectionUtils#addIgnoreNull(Collection, Object)". Added missing null check in "CollectionUtils#addIgnoreNull(Collection, Object)".

51
src/main/java/org/apache/commons/collections4/ListUtils.java
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@ -30,6 +30,9 @@ import org.apache.commons.collections4.list.LazyList;
import org.apache.commons.collections4.list.PredicatedList; import org.apache.commons.collections4.list.PredicatedList;
import org.apache.commons.collections4.list.TransformedList; import org.apache.commons.collections4.list.TransformedList;
import org.apache.commons.collections4.list.UnmodifiableList; import org.apache.commons.collections4.list.UnmodifiableList;
import org.apache.commons.collections4.sequence.CommandVisitor;
import org.apache.commons.collections4.sequence.EditScript;
import org.apache.commons.collections4.sequence.SequencesComparator;
/** /**
* Provides utility methods and decorators for {@link List} instances. * Provides utility methods and decorators for {@link List} instances.
@ -489,6 +492,7 @@ public class ListUtils {
return FixedSizeList.fixedSizeList(list); return FixedSizeList.fixedSizeList(list);
} }
//-----------------------------------------------------------------------
/** /**
* Finds the first index in the given List which matches the given predicate. * Finds the first index in the given List which matches the given predicate.
* <p> * <p>
@ -512,6 +516,53 @@ public class ListUtils {
return -1; return -1;
} }
//-----------------------------------------------------------------------
/**
* Returns the longest common subsequence (LCS) of two sequences (lists).
*
* @param <T> the element type
* @param a the first list
* @param b the second list
* @return the longest common subsequence
* @throws IllegalArgumentException if either list is {@code null}
* @since 4.0
*/
public static <T> List<T> longestCommonSubsequence(final List<T> a, final List<T> b) {
if (a == null || b == null) {
throw new IllegalArgumentException("List must not be null");
}
final SequencesComparator<T> comparator = new SequencesComparator<T>(a, b);
final EditScript<T> script = comparator.getScript();
final LcsVisitor<T> visitor = new LcsVisitor<T>();
script.visit(visitor);
return visitor.getSubSequence();
}
/**
* A helper class used to construct the longest common subsequence.
*/
private static final class LcsVisitor<E> implements CommandVisitor<E> {
private ArrayList<E> sequence;
public LcsVisitor() {
sequence = new ArrayList<E>();
}
public void visitInsertCommand(final E object) {}
public void visitDeleteCommand(final E object) {}
public void visitKeepCommand(final E object) {
sequence.add(object);
}
public List<E> getSubSequence() {
return sequence;
}
}
//-----------------------------------------------------------------------
/** /**
* Returns consecutive {@link List#subList(int, int) sublists} of a * Returns consecutive {@link List#subList(int, int) sublists} of a
* list, each of the same size (the final list may be smaller). For example, * list, each of the same size (the final list may be smaller). For example,

41
src/test/java/org/apache/commons/collections4/ListUtilsTest.java
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@ -31,6 +31,7 @@ import org.apache.commons.collections4.ListUtils;
import org.apache.commons.collections4.Predicate; import org.apache.commons.collections4.Predicate;
import org.apache.commons.collections4.functors.EqualPredicate; import org.apache.commons.collections4.functors.EqualPredicate;
import org.apache.commons.collections4.list.PredicatedList; import org.apache.commons.collections4.list.PredicatedList;
import org.junit.Assert;
/** /**
* Tests for ListUtils. * Tests for ListUtils.
@ -311,6 +312,46 @@ public class ListUtilsTest extends BulkTest {
assertEquals(ListUtils.indexOf(fullList, null), -1); assertEquals(ListUtils.indexOf(fullList, null), -1);
} }
public void testLongestCommonSubsequence() {
try {
ListUtils.longestCommonSubsequence(null, null);
fail("failed to check for null argument");
} catch (final IllegalArgumentException e) {}
try {
ListUtils.longestCommonSubsequence(Arrays.asList('A'), null);
fail("failed to check for null argument");
} catch (final IllegalArgumentException e) {}
try {
ListUtils.longestCommonSubsequence(null, Arrays.asList('A'));
fail("failed to check for null argument");
} catch (final IllegalArgumentException e) {}
@SuppressWarnings("unchecked")
List<Character> lcs = ListUtils.longestCommonSubsequence(Collections.EMPTY_LIST, Collections.EMPTY_LIST);
assertTrue(lcs.isEmpty());
List<Character> list1 = Arrays.asList('B', 'A', 'N', 'A', 'N', 'A');
List<Character> list2 = Arrays.asList('A', 'N', 'A', 'N', 'A', 'S');
lcs = ListUtils.longestCommonSubsequence(list1, list2);
List<Character> expected = Arrays.asList('A', 'N', 'A', 'N', 'A');
assertEquals(expected, lcs);
List<Character> list3 = Arrays.asList('A', 'T', 'A', 'N', 'A');
lcs = ListUtils.longestCommonSubsequence(list1, list3);
expected = Arrays.asList('A', 'A', 'N', 'A');
assertEquals(expected, lcs);
List<Character> listZorro = Arrays.asList('Z', 'O', 'R', 'R', 'O');
lcs = ListUtils.longestCommonSubsequence(list1, listZorro);
assertTrue(lcs.isEmpty());
}
public void testPartition() { public void testPartition() {
final List<Integer> strings = new ArrayList<Integer>(); final List<Integer> strings = new ArrayList<Integer>();
for (int i = 0; i <= 6; i++) { for (int i = 0; i <= 6; i++) {