算法：在一个集合中选取所有符合条件的元素组合

[code]import org.junit.Test;

import java.util.ArrayList;
import java.util.List;

public class JunitTest {

    @Test
    public void test() throws InterruptedException {
        List<Integer> testList = new ArrayList<Integer>();
        testList.add(5);
        testList.add(10);
        testList.add(15);
        testList.add(20);
        testList.add(25);
        testList.add(30);
        testList.add(35);

        System.out.println(select(40, 60, 3, testList));
    }

    //递归选择指定个数　符合条件的所有组合
    private List<List<Integer>> select(int min, int max, int count, List<Integer> resourceList) {
        if (count == 1) {
            return eligible(min, max, resourceList);
        } else {
            List<List<Integer>> rsList = new ArrayList<List<Integer>>();

            Integer i = resourceList.remove(0);

            if (resourceList.size() >= count) {
                List<Integer> tmpList = new ArrayList<Integer>(resourceList);
                //去掉第一个元素 剩余元素中的组合
                rsList.addAll(select(min, max, count, tmpList));
            }
            //个数--，条件拆分 min - i, max - i
            rsList.addAll(assembly(i, select(min - i, max - i, --count, resourceList)));
            return rsList;
        }
    }

    //选择符合条件的结果
    private List<List<Integer>> eligible(int min, int max, List<Integer> resourceList) {
        List<List<Integer>> rsList = new ArrayList<List<Integer>>();
        for (Integer i : resourceList) {
            if (i >= min && i <= max) {
                List<Integer> tmp = new ArrayList<Integer>();
                tmp.add(i);
                rsList.add(tmp);
            }
        }
        return rsList;
    }

    //组合
    private List<List<Integer>> assembly(Integer base, List<List<Integer>> resourceList) {
        List<List<Integer>> rsList = new ArrayList<List<Integer>>();

        for (List<Integer> list : resourceList) {
            list.add(base);
            rsList.add(list);
        }

        return rsList;
    }
}