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 test
int[] 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 test
String[] 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;
} @Override
public boolean hasNext() {
return _bitArray[_length + 1] != 1;
} @SuppressWarnings("unchecked")
@Override
public 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();
}
}