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( All code listed in this article is included in my personal lib, and the repo is hosted at: https://github.com/raistlic/LibRaistCommon )
最近在整理个人代码，有些觉得可能有用的，拿出来共享一下 
先上用法示例代码：
问题一： 有三个字符串 "a", "b", "c"，进行排列，列出共有多少种排列方式
public class PNCDemo {
public static void main(String[] args) {
System.out.println("===== demo permutation :");
for(List<String> list : Permutation.of(Arrays.asList("a", "b", "c")))
System.out.println(list);
}
}run:
===== demo permutation :
[a, b, c]
[a, c, b]
[b, a, c]
[b, c, a]
[c, a, b]
[c, b, a]
BUILD SUCCESSFUL (total time: 0 seconds)
问题二： 从五个数 1, 2, 3, 4, 5 中任取 3 个数，列出共有多少种取法
public class PNCDemo {
public static void main(String[] args) {
System.out.println("===== demo combination :");
for(List<Integer> list : Combination.of(Arrays.asList(1, 2, 3, 4, 5), 3))
System.out.println(list);
}
}问题三： 从五个数 1, 2, 3, 4, 5 中任取 3 个数进行排列，列出共有多少种排列方式
public class PNCDemo {
public static void main(String[] args) {
System.out.println("===== demo both :");
for(List<Integer> list : Permutation.of(Arrays.asList(1, 2, 3, 4, 5), 3))
System.out.println(list);
}
}run:
===== demo both :
[1, 2, 3]
[1, 3, 2]
[2, 1, 3]
[2, 3, 1]
[3, 1, 2]
[3, 2, 1]
[1, 2, 4]
[1, 4, 2]
[2, 1, 4]
[2, 4, 1]
[4, 1, 2]
[4, 2, 1]
[1, 2, 5]
[1, 5, 2]
[2, 1, 5]
[2, 5, 1]
[5, 1, 2]
[5, 2, 1]
[1, 3, 4]
[1, 4, 3]
[3, 1, 4]
[3, 4, 1]
[4, 1, 3]
[4, 3, 1]
[1, 3, 5]
[1, 5, 3]
[3, 1, 5]
[3, 5, 1]
[5, 1, 3]
[5, 3, 1]
[1, 4, 5]
[1, 5, 4]
[4, 1, 5]
[4, 5, 1]
[5, 1, 4]
[5, 4, 1]
[2, 3, 4]
[2, 4, 3]
[3, 2, 4]
[3, 4, 2]
[4, 2, 3]
[4, 3, 2]
[2, 3, 5]
[2, 5, 3]
[3, 2, 5]
[3, 5, 2]
[5, 2, 3]
[5, 3, 2]
[2, 4, 5]
[2, 5, 4]
[4, 2, 5]
[4, 5, 2]
[5, 2, 4]
[5, 4, 2]
[3, 4, 5]
[3, 5, 4]
[4, 3, 5]
[4, 5, 3]
[5, 3, 4]
[5, 4, 3]
BUILD SUCCESSFUL (total time: 0 seconds)
话说算法这种东西，似乎天生适合写成“策略接口” ———— 夫算法者，策略者也。
第一个文件： 排列和组合都要用到的阶乘类（原类名没有改，去掉了与本题无关的部分）
/*
* Copyright 2012 wuyou (raistlic@gmail.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.
*/
import java.math.BigInteger;
/**
* This class is intended to provide convenient facilities for
* frequently used maths calculations that {@code java.lang.Math}
* does not cover.
*
* @date 08/08/2012
*/
public final class Calculator {
private Calculator() {}
private static final BigInteger[] FACT_RESULT_POOL = new BigInteger[1024];
public static BigInteger factorial(int number) {
if( number < 0 )
throw new IllegalArgumentException();
BigInteger result = null;
if( number < FACT_RESULT_POOL.length )
result = FACT_RESULT_POOL[number];
if( result == null ) {
result = BigInteger.ONE;
for(int i = 2; i <= number; i++)
result = result.multiply(BigInteger.valueOf(i));
if( number < FACT_RESULT_POOL.length )
FACT_RESULT_POOL[number] = result;
}
return result;
}
}
/*
* Copyright 2012 wuyou (raistlic@gmail.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.
*/
import java.math.BigInteger;
/**
* The strategy interface for implementing the combination algorithm.
*
* @date 07/08/2012
*/
public interface CombinationAlgorithm {
public int getMaxSupportedSize();
public BigInteger getCombinationCount(int numberOfElements, int numberToPick);
public void fetchCombination(Object[] source, Object[] target, BigInteger ordinal);
}
/*
* Copyright 2012 wuyou (raistlic@gmail.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.
*/
import java.math.BigInteger;
import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import static java.math.BigInteger.ONE;
import static java.math.BigInteger.ZERO;
/**
* This class is to fulfill the needs of getting combinations from a
* collection.
*
* It basically provides the functionalities of :
* 1 - enquiry the number of combination count : c(m, n)
* 2 - given an ordinal number i, fetch the i-th combination of c(m, n)
* as a read-only list.
* 3 - convenient for-each iteration of all the combinations
*
* This class is NOT thread safe.
*
* This class re-uses one array to fetch the combination, so if the user
* want to keep the i-th combination result, make a copy.
*
* @date 07/08/2012
* @author raistlic
*/
public class Combination<E> implements Iterable<List<E>> {
public static final CombinationAlgorithm DEFAULT_ALGORITHM =
AlgorithmVER01.INSTANCE;
public static <E> Combination<E> of(Collection<E> elements,
int numberToPick) {
return of(elements, numberToPick, DEFAULT_ALGORITHM);
}
public static <E> Combination<E> of(Collection<E> elements,
int numberToPick,
CombinationAlgorithm algorithm) {
if( elements == null )
throw new NullPointerException();
if( numberToPick < 0 || numberToPick > elements.size() )
throw new IllegalArgumentException(
"Invalid number of elements to pick : " + numberToPick +
" out of " + elements.size());
if( algorithm == null )
algorithm = DEFAULT_ALGORITHM;
return new Combination<E>(elements, numberToPick, algorithm);
}
@SuppressWarnings("unchecked")
private E[] elements, picked;
private CombinationAlgorithm algorithm;
private BigInteger count;
private Combination(Collection<E> elements,
int numberToPick,
CombinationAlgorithm algorithm) {
assert elements != null;
assert numberToPick >= 0;
assert numberToPick <= elements.size();
assert algorithm != null;
this.elements = (E[])elements.toArray();
this.picked = (E[])new Object[numberToPick];
this.algorithm = algorithm;
this.count = this.algorithm.getCombinationCount(
this.elements.length, numberToPick);
}
public BigInteger getCombinationCount() {
return count;
}
public List<E> getCombination(BigInteger ordinal) {
algorithm.fetchCombination(elements, picked, ordinal);
return Arrays.asList(picked);
}
@Override
public Iterator<List<E>> iterator() {
return new OrdinalIterator();
}
private class OrdinalIterator implements Iterator<List<E>> {
private BigInteger ordinal;
private OrdinalIterator() {
ordinal = ZERO;
}
@Override
public boolean hasNext() {
return ordinal.compareTo(getCombinationCount()) < 0;
}
@Override
public List<E> next() {
List<E> result = getCombination(ordinal);
ordinal = ordinal.add(ONE);
return result;
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
}
private static enum AlgorithmVER01 implements CombinationAlgorithm {
INSTANCE;
@Override
public int getMaxSupportedSize() {
return MAX_SUPPORT;
}
@Override
public BigInteger getCombinationCount(int numberOfElements, int numberToPick) {
if( numberOfElements < 0 )
throw new IllegalArgumentException(
"Invalid number of elements : " + numberOfElements);
if( numberOfElements > getMaxSupportedSize() )
throw new IllegalArgumentException(
"Number of elements out of range : " + numberOfElements);
if( numberToPick < 0 || numberToPick > numberOfElements )
throw new IllegalArgumentException(
"Invalid number to pick : " + numberToPick);
if( numberToPick == 0 || numberToPick == numberOfElements)
return ONE;
else
return Calculator.factorial(numberOfElements).divide(
Calculator.factorial(numberToPick).multiply(
Calculator.factorial(numberOfElements - numberToPick)));
}
@Override
public void fetchCombination(Object[] source,
Object[] target,
BigInteger ordinal) {
for(int i=0, si=0; i<target.length; i++, si++) {
if( ordinal.compareTo(ZERO) > 0 ) {
BigInteger cLeft = getCombinationCount(
source.length - si - 1, target.length - i - 1);
while( ordinal.compareTo(cLeft) >= 0 ) {
si++;
ordinal = ordinal.subtract(cLeft);
if( ordinal.compareTo(ZERO) == 0 )
break;
cLeft = getCombinationCount(
source.length - si - 1, target.length - i - 1);
}
}
target[i] = source[si];
}
}
private static final int MAX_SUPPORT = 1024;
}
}
第四个文件： 定义了“排列算法”要做的事情的 ——策略接口
/*
* Copyright 2012 wuyou (raistlic@gmail.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.
*/
import java.math.BigInteger;
/**
* The strategy interface for implementing the permutation algorithm.
*
* @date 07/08/2012
*/
public interface PermutationAlgorithm {
public int getMaxSupportedSize();
public BigInteger getPermutationCount(int numberOfElements);
public void fetchPermutation(Object[] elements, BigInteger ordinal);
}
/*
* Copyright 2012 wuyou (raistlic@gmail.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.
*/
import java.math.BigInteger;
import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import static java.math.BigInteger.ONE;
import static java.math.BigInteger.ZERO;
/**
* This class is to fulfill the needs of getting permutations from a
* collection.
*
* It basically provides the functionalities of :
* 1 - enquiry the number of permutation count : p(m, n)
* 2 - given an ordinal number i, fetch the i-th permutation result
* as a read-only list.
* 3 - convenient for-each iteration of all the permutations
*
* This class is NOT thread safe.
*
* This class re-uses one array to fetch each enquiry, so if the user
* want to keep the i-th permutation result, make a copy.
*
* @date 07/08/2012
* @author raistlic
*/
public class Permutation<E> implements Iterable<List<E>>{
public static final PermutationAlgorithm DEFAULT_PERMUTATION_ALGORITHM =
AlgorithmVER01.INSTANCE;
public static final CombinationAlgorithm DEFAULT_COMBINATION_ALGORITHM =
Combination.DEFAULT_ALGORITHM;
public static <E> Permutation<E> of(Collection<E> elements) {
return of(elements, elements.size());
}
public static <E> Permutation<E> of(Collection<E> elements,
int numberToPick) {
return of(elements, numberToPick, DEFAULT_PERMUTATION_ALGORITHM);
}
public static <E> Permutation<E> of(Collection<E> elements,
PermutationAlgorithm pAlgorithm) {
return of(elements, elements.size(), pAlgorithm);
}
public static <E> Permutation<E> of(Collection<E> elements,
int numberToPick,
PermutationAlgorithm pAlgorithm) {
return of(elements, numberToPick, pAlgorithm, DEFAULT_COMBINATION_ALGORITHM);
}
public static <E> Permutation<E> of(Collection<E> elements,
int numberToPick,
PermutationAlgorithm pAlgorithm,
CombinationAlgorithm cAlgorithm) {
if( elements == null )
throw new NullPointerException();
if( pAlgorithm == null )
throw new NullPointerException();
if( elements.size() > pAlgorithm.getMaxSupportedSize() )
throw new IllegalArgumentException(
"Element collection size not supported by the permutation algorithm.");
return new Permutation<E>(elements, numberToPick, pAlgorithm, cAlgorithm);
}
@SuppressWarnings("unchecked")
private E[] elements, picked;
private PermutationAlgorithm pAlgorithm;
private CombinationAlgorithm cAlgorithm;
private BigInteger cCount, pCount;
private BigInteger count;
private int numberToPick;
private Permutation(Collection<E> elements,
int numberToPick,
PermutationAlgorithm pAlgorithm,
CombinationAlgorithm cAlgorithm) {
assert elements != null;
assert pAlgorithm != null;
assert cAlgorithm != null;
assert numberToPick >= 0;
assert numberToPick <= elements.size();
this.elements = (E[])elements.toArray();
this.picked = (E[])new Object[numberToPick];
this.pAlgorithm = pAlgorithm;
this.cAlgorithm = cAlgorithm;
this.numberToPick = numberToPick;
this.cCount = this.cAlgorithm.getCombinationCount(this.elements.length,
this.numberToPick);
this.pCount = this.pAlgorithm.getPermutationCount(this.numberToPick);
this.count = this.cCount.multiply(this.pCount);
}
public BigInteger getPermutationCount() {
return count;
}
public List<E> getPermutation(BigInteger ordinal) {
if( ordinal == null )
throw new NullPointerException();
if( ordinal.compareTo(ZERO) < 0 || ordinal.compareTo(count) >= 0 )
throw new IllegalArgumentException(
"Ordinal value out of range : " + ordinal);
if( numberToPick == elements.length ) {
System.arraycopy(elements, 0, picked, 0, elements.length);
}
else {
cAlgorithm.fetchCombination(elements, picked, ordinal.divide(pCount));
ordinal = ordinal.mod(pCount);
}
pAlgorithm.fetchPermutation(picked, ordinal);
return Arrays.asList(picked);
}
@Override
public Iterator<List<E>> iterator() {
return this.new OrdinalIterator();
}
private class OrdinalIterator implements Iterator<List<E>> {
private BigInteger ordinal;
private OrdinalIterator() {
this.ordinal = ZERO;
}
@Override
public boolean hasNext() {
return ordinal.compareTo(count) < 0;
}
@Override
public List<E> next() {
List<E> result = getPermutation(ordinal);
ordinal = ordinal.add(ONE);
return result;
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
}
private static enum AlgorithmVER01 implements PermutationAlgorithm {
INSTANCE;
@Override
public int getMaxSupportedSize() {
return MAX_SUPPORT;
}
@Override
public BigInteger getPermutationCount(int numberOfElements) {
if( numberOfElements < 0 )
throw new IllegalArgumentException(
"Invalid number of elements : " + numberOfElements);
if( numberOfElements > getMaxSupportedSize() )
throw new IllegalArgumentException(
"Number of elements out of range : " + numberOfElements);
return Calculator.factorial(numberOfElements);
}
@Override
public void fetchPermutation(Object[] elements, BigInteger ordinal) {
for(int i=0; i<elements.length-1; i++) {
int left = elements.length - i - 1;
BigInteger leftCount = Calculator.factorial(left);
int curr = ordinal.divide(leftCount).intValue();
ordinal = ordinal.mod(leftCount);
if( curr > 0 ) {
Object temp = elements[curr + i];
for(int j = curr + i; j > i; j--)
elements[j] = elements[j - 1];
elements[i] = temp;
}
}
}
private static final int MAX_SUPPORT = 1024;
}
}
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