JAVA求集合中的组合

好几个月没弄代码了，今天弄个求组合的DEMO

思路是将集合的每个值对照一个索引，索引大小是集合的大小+2.索引默认为[000...000]，当组合后选取的组合值demo为[0100..00]。然后根据遍历索引来到集合中取值。

上代码：

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;public class ComBit {public static void main(String[] args) {// Integer testint[] combination = new int[] { 1, 2, 3, 4 };List<Integer> combinationlist = new ArrayList<Integer>();for (Integer integer : combination) {combinationlist.add(integer);}ComBitIterator<Integer> i = new ComBitIterator<Integer>(combinationlist);while (i.hasNext()) {Object obj = i.next();System.out.println(obj.toString());}// String testString[] str = new String[] { "apple", "orange", "tomato", "potato" };List<String> combinationSlist = new ArrayList<String>();for (String s : str) {combinationSlist.add(s);}ComBitIterator<String> ii = new ComBitIterator<String>(combinationSlist);while (ii.hasNext()) {Object obj = ii.next();System.out.println(obj.toString());}}}class ComBitIterator<T> implements Iterator<T> {private int[] _bitArray = null;protected final int _length;protected final List<T> combination;protected List<T> _currentSet;public ComBitIterator(List<T> combination) {_currentSet = new ArrayList<T>();this._length = combination.size();this._bitArray = new int[_length + 2];this.combination = combination;}@Overridepublic boolean hasNext() {return _bitArray[_length + 1] != 1;}@SuppressWarnings("unchecked")@Overridepublic T next() {_currentSet.clear();for (int index = 1; index <= _length; index++) {if (_bitArray[index] == 1) {T value = combination.get(index - 1);_currentSet.add(value);}}int i = 1;while (_bitArray[i] == 1) {_bitArray[i] = 0;i++;}_bitArray[i] = 1;return (T) _currentSet;}}

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PS:代码源于要求求数字1-20中 任取N的组合后合值为36，于是思路想到两种，第一种是递归，第二种虽然也是递归，但是想弄个通用的，就有了以上的代码。另外群里有人写出了直接递归的代码，也附上：

public static void main(String[] args) {combinateDataOfRange(1, 20, 36);}public static void combinateDataOfRange(int min, int max, int target) {combinateData(0, min, max, target, new Stack<Integer>());}public static void combinateData(int sum, int min, int max, int target,Stack<Integer> stack) {for (int i = stack.isEmpty() ? min : (Integer) stack.lastElement() + 1; i < max; ++i) {int tempSum = sum + i;stack.push(i);if (tempSum == target) {System.out.println(stack + "=" + target);} else {combinateData(tempSum, min, max, target, stack);}stack.pop();}}