/**

• 递归

• @Author Allen

• @Description

• @Date 2018/10/18 10:42
  **/
  public class RecursionTest {

  private static final Logger logger = LoggerFactory.getLogger(RecursionTest.class);

  /**

  • @Description: 罗列一个集合 n个元素的组合

  • @param group 组合结果, 原始集合, 组合长度
    */
    public void groupCreater(List allGroup, List group, List list, Integer len) {

    if (len <= 0) {
    logger.info(group.toString());
    allGroup.add(group);
    logger.info(allGroup.toString());
    return;
    }

    // 考虑list为空的情况
    if (list.isEmpty()) {
    return;
    }

    // 假设选取第一个元素
    group.add(list.get(0));
    groupCreater(allGroup, group, list.subList(1, list.size()), len - 1);

    // 假设没有选取第一个元素
    group.remove(group.size() - 1);
    groupCreater(allGroup, group, list.subList(1, list.size()), len);

  }

  public static void main(String[] args) {
  RecursionTest test = new RecursionTest();
  List allGroups = new ArrayList();

// logger.info("-----------------");
// test.groupCreater(allGroups,new ArrayList(), new ArrayList(), 0);
// logger.info(JSON.toJSONString(allGroups));
// allGroups.clear();
//
logger.info("-----------------");
test.groupCreater(allGroups, new ArrayList(), Arrays.asList(1, 2, 3, 4), 2);
logger.info(allGroups.toString());

// logger.info("-----------------");
// test.groupCreater(allGroups, new ArrayList(), Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10), 5);
// logger.info(JSON.toJSONString(allGroups));
// allGroups.clear();

}

}