技术标签: 算法
JDK,Apache commons math里都没有发现组合函数,因而自己写了一个。
首先定义接口
package math.combination;
import java.util.Collection;
import java.util.List;
/**
* the interface for combination
* @author jhren
*
* @param <T>
*/
public interface Combinationable<T> {
/**
* get combinations from start to end [start, end]
* it equals findCombiantions(start),findCombiantions(start+1),
* ......
* findCombinations(end-1), findCombinations(end)
*/
public List<List<T>> findCombinations(int start, int end);
/**
* get all combinations
* it equals findCombinations(0, size)
*/
public List<List<T>> findCombinations();
/**
* find a combinations for size
* @param size
* @return
*/
public List<List<T>> findCombinations(int size);
public Collection<T> getElements();
}
第一个个实现,输出的组合会按照类型T升序排列
例如输入为[3,2,1]的全组合为
[]
[3]
[2]
[1]
[2, 3]
[1, 3]
[1, 2]
[1, 2, 3]
package math.combination;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
/**
* the T should be Comparable the T in one combination list is sort by the
* Comparable T
*
* @author jhren
*
* @param <T>
*/
public class ComparableCombination<T extends Comparable<? super T>> implements
Combinationable<T> {
private Collection<T> elements = new ArrayList<T>();
public ComparableCombination(Collection<T> elements) {
this.elements.addAll(elements);
}
@Override
public List<List<T>> findCombinations(int start, int end) {
if (start < 0) {
throw new IllegalArgumentException("start can't be negative: "
+ start);
}
if (end > elements.size()) {
throw new IllegalArgumentException(
"end can't be larger than elements size: " + end + ">"
+ elements.size());
}
if(start > end) {
throw new IllegalArgumentException(
"start can't be larger than end: " + start + ">"
+ end);
}
List<List<T>> result = new ArrayList<List<T>>();
for (int i = start; i <= end; i++) {
result.addAll(findCombinations(i));
}
return result;
}
@Override
public List<List<T>> findCombinations() {
return findCombinations(0, elements.size());
}
@Override
public List<List<T>> findCombinations(int size) {
if (size < 0) {
throw new IllegalArgumentException("size can't be negative: "
+ size);
}
if (size > elements.size()) {
throw new IllegalArgumentException(
"size can't be larger than elements size: " + size + ">"
+ elements.size());
}
List<List<T>> result = new ArrayList<List<T>>();
if (size == 0) {
result.add(new ArrayList<T>());
return result;
}
List<List<T>> combinations = findCombinations(size - 1);
for (List<T> combination : combinations) {
for (T element : elements) {
if (combination.contains(element)) {
continue;
}
List<T> list = new ArrayList<T>();
list.addAll(combination);
if (list.contains(element))
continue;
list.add(element);
Collections.sort(list);
if (result.contains(list))
continue;
result.add(list);
}
}
return result;
}
@Override
public Collection<T> getElements() {
return elements;
}
}
例如输入为[3,2,1]的全组合为
[]
[3]
[2]
[1]
[3, 2]
[3, 1]
[2, 1]
[3, 2, 1]
package math.combination;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
/**
* the T in one combination list is sort by the input sequence
* @author jhren
*
* @param <T>
*/
public class CombinationSortByInput<T> implements Combinationable<T> {
static private class Element<E> implements Comparable<Element<E>> {
private int rank;
private E e;
public E getE() {
return e;
}
private Element(E e, int rank) {
this.e = e;
this.rank = rank;
}
@Override
public int compareTo(Element<E> o) {
return this.rank - o.rank;
}
}
private Combinationable<Element<T>> combination = null;
public CombinationSortByInput(Collection<T> elements) {
Collection<Element<T>> elementsInput = convertCollection(elements);
combination = new ComparableCombination<Element<T>>(elementsInput);
}
@Override
public List<List<T>> findCombinations(int start, int end) {
List<List<Element<T>>> elementsOutput = combination.findCombinations(start, end);
List<List<T>> output = convertListOfList(elementsOutput);
return output;
}
@Override
public List<List<T>> findCombinations() {
return findCombinations(0, combination.getElements().size());
}
@Override
public List<List<T>> findCombinations(int size) {
return findCombinations(size,size);
}
private static <T> Collection<Element<T>> convertCollection(Collection<T> input) {
Collection<Element<T>> elementCollectionInput = new ArrayList<Element<T>>();
Iterator<T> iterator = input.iterator();
int i = 0;
while(iterator.hasNext()) {
T t = iterator.next();
Element<T> element = new Element<T>(t, i++);
elementCollectionInput.add(element);
}
return elementCollectionInput;
}
private static <T> List<List<T>> convertListOfList(
List<List<Element<T>>> elementsOutput) {
List<List<T>> output = new ArrayList<List<T>>();
for(List<Element<T>> elementList : elementsOutput) {
List<T> tlist = convertList(elementList);
output.add(tlist);
}
return output;
}
private static <T> List<T> convertList(Collection<Element<T>> elementList) {
List<T> tlist = new ArrayList<T>();
for(Element<T> element: elementList) {
T t = element.getE();
tlist.add(t);
}
return tlist;
}
@Override
public Collection<T> getElements() {
return convertList(combination.getElements());
}
}
package math.combination;
import java.util.Arrays;
import java.util.List;
import math.combination.Combinationable;
import math.combination.ComparableCombination;
import org.testng.annotations.Test;
import org.testng.annotations.BeforeClass;
import static org.testng.AssertJUnit.assertNotNull;
import static org.testng.AssertJUnit.assertEquals;
import static org.testng.AssertJUnit.assertTrue;
public class TestComparableCombination {
private Combinationable<Integer> combination= null;
@Test
public void testGetElements() {
assertNotNull(combination.getElements());
assertEquals(3, combination.getElements().size());
}
@Test
public void testFindCombinationsSizeZero() {
List<List<Integer>> lists = combination.findCombinations(0);
assertNotNull(lists);
assertEquals(1, lists.size());
assertNotNull(lists.get(0));
assertEquals(0, lists.get(0).size());
}
@Test (expectedExceptions = IllegalArgumentException.class)
public void testFindCombinationsSizeMinus() {
combination.findCombinations(-1);
}
@Test (expectedExceptions = IllegalArgumentException.class)
public void testFindCombinationsStartMinus() {
combination.findCombinations(-1,2);
}
@Test (expectedExceptions = IllegalArgumentException.class)
public void testFindCombinationsSizeOverflow() {
combination.findCombinations(combination.getElements().size() + 1);
}
@Test (expectedExceptions = IllegalArgumentException.class)
public void testFindCombinationsEndOverflow() {
combination.findCombinations(0,combination.getElements().size() + 1);
}
@Test (expectedExceptions = IllegalArgumentException.class)
public void testFindCombinationsStartEndWrongOrder() {
combination.findCombinations(1,0);
}
@Test
public void testFindCombinationsSizeTwo() {
List<List<Integer>> lists = combination.findCombinations(2);
assertNotNull(lists);
assertEquals(3, lists.size());
for(List<Integer> list: lists) {
assertEquals(2, list.size());
int element0 = list.get(0);
int elements1 = list.get(1);
assertTrue(element0 < elements1);
}
}
@Test
public void testFindAllCombinations1() {
List<List<Integer>> lists = combination.findCombinations();
assertNotNull(lists);
assertEquals(8, lists.size());
for(List<Integer> list : lists) {
System.out.println(list);
}
}
@Test
public void testFindAllCombinations2() {
List<List<Integer>> lists = combination.findCombinations(0, combination.getElements().size());
assertNotNull(lists);
assertEquals(8, lists.size());
}
@Test(timeOut=20000)
public void testPerformance() {
combination = new ComparableCombination<Integer>(Arrays.asList(3,2,1,4,5));
for(int i = 0;i < 100000; i++) {
combination.findCombinations();
}
}
@BeforeClass
public void beforeClass() {
combination = new ComparableCombination<Integer>(Arrays.asList(3,2,1));
}
}
package math.combination;
import java.util.Arrays;
import java.util.List;
import math.combination.CombinationSortByInput;
import math.combination.Combinationable;
import org.testng.annotations.Test;
import org.testng.annotations.BeforeClass;
import static org.testng.AssertJUnit.assertNotNull;
import static org.testng.AssertJUnit.assertEquals;
import static org.testng.AssertJUnit.assertTrue;
public class TestCombinationSortByInput {
private Combinationable<Integer> combination= null;
@Test
public void testGetElements() {
assertNotNull(combination.getElements());
assertEquals(3, combination.getElements().size());
}
@Test
public void testFindCombinationsSizeZero() {
List<List<Integer>> lists = combination.findCombinations(0);
assertNotNull(lists);
assertEquals(1, lists.size());
assertNotNull(lists.get(0));
assertEquals(0, lists.get(0).size());
}
@Test (expectedExceptions = IllegalArgumentException.class)
public void testFindCombinationsSizeMinus() {
combination.findCombinations(-1);
}
@Test (expectedExceptions = IllegalArgumentException.class)
public void testFindCombinationsSizeOverflow() {
combination.findCombinations(combination.getElements().size() + 1);
}
@Test
public void testFindCombinationsSizeTwo() {
List<List<Integer>> lists = combination.findCombinations(2);
assertNotNull(lists);
assertEquals(3, lists.size());
for(List<Integer> list: lists) {
assertEquals(2, list.size());
int element0 = list.get(0);
int elements1 = list.get(1);
assertTrue(element0 > elements1);
}
}
@Test
public void testFindAllCombinations1() {
List<List<Integer>> lists = combination.findCombinations();
assertNotNull(lists);
assertEquals(8, lists.size());
for(List<Integer> list : lists) {
System.out.println(list);
}
}
@Test
public void testFindAllCombinations2() {
List<List<Integer>> lists = combination.findCombinations(0, combination.getElements().size());
assertNotNull(lists);
assertEquals(8, lists.size());
}
@BeforeClass
public void beforeClass() {
combination = new CombinationSortByInput<Integer>(Arrays.asList(3,2,1));
}
@Test(timeOut=20000)
public void testPerformance() {
combination = new CombinationSortByInput<Integer>(Arrays.asList(3,2,1,4,5));
for(int i = 0;i < 100000; i++) {
combination.findCombinations();
}
}
}
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