java - 查找递归 void 方法的基本情况

Question

我正在做作业。我想为递归建立一个基本案例，其中按升序排列给定数字(list2)。编写这段代码的目的是，当所有数字都按升序排列时，应停止调用名为 ascending(list2, list1) 的方法； list2 中的所有值都应发送到 list1。例如，list2 = 6,5,4,3,2,1 那么 list2 变为空，list1 应该是 1,2,3,4,5,6。我正在尝试将结果与前一个进行比较，如果匹配则停止。但我找不到阻止它的基本案例。另外，ascending() 和 fixedPoint() 都是 void 方法。有人有想法吗？大声笑花了我 3 天...

然后当我运行我的代码时

6,5,4,3,2,1

5,6,4,3,2,1

4,5,6,3,2,1

3,4,5,6,2,1

2,3,4,5,6,1

1,2,3,4,5,6

1,2,3,4,5,6

1,2,3,4,5,6

1,2,3,4,5,6

1,2,3,4,5,6

无限......

public class Flipper
{
public static void main(String[] args)
{   
    Flipper aFlipper = new Flipper();

    List<Integer> content = Arrays.asList(6,5,4,3,2,1);
    ArrayList<Integer> l1 =  new ArrayList<Integer>(content);
    ArrayList<Integer> l2 = new ArrayList<Integer>(); // empty list

    aFlipper.fixedPoint(l2,l1);

    System.out.println("fix   l1 is "+l1);
    System.out.println("fix   l2 is "+l2);
}
public void fixedPoint(ArrayList<Integer> list1, ArrayList<Integer> list2)
{
    // data is in list2
    ArrayList<Integer> temp1 = new ArrayList<Integer>(); // empty list

    if (temp1.equals(list2)) 
    {
        System.out.println("found!!!");             
    }

    else
    {
        ascending(list2, list1); // data, null
        temp1 = list1; // store processed value
        System.out.println("st list1 is "+list1);
        System.out.println("st list2 is "+list2);
    }
    fixedPoint(list2, list1); // null, processed data       
}

收到建议后的第二次尝试。

else        {
            temp1 = list2;
            System.out.println("temp1: "+temp1); 

//temp1打印出赋值

            // store only previous value
            ascending(list2, list1); // data, null

            temp2 = list1;
            // store previous value

            System.out.println("temp1: "+temp1); 

//在调用 ascending() temp1 之后变成空的 大声笑 所以无法在 if 语句中进行比较....有人可以更正吗？

            System.out.println("temp2: "+temp2);
        }
        fixedPoint(list2, list1); // previous, proceeded data

在与 dasblinkenlight、Julien S、Nikolas、ZouZou 和 vels4j 进行头脑 Storm 之后，找到了解决方案。感谢您的思想贡献! :-)

public void fixedPoint(ArrayList<Integer> list1, 
                       ArrayList<Integer> list2)
    {
        List<Integer> content = Arrays.asList(1);
        ArrayList<Integer> temp1 = new ArrayList<Integer>(content); 
        fixedPoint(list2, list1, temp1);
    }
    // Since it is recursive method I needed to create another parameter
    // to store temporary values.
    public void fixedPoint(ArrayList<Integer> list1, 
                           ArrayList<Integer> list2, 
                           ArrayList<Integer> temp)
    {


        ArrayList<Integer> temp1 = new ArrayList<Integer>();
        temp1 = temp;

        if (temp1.equals(list2))
        {
            return;
        }

        else
        {
            temp1.clear(); 
            for(int i = 0; i < list2.size(); i++) 
            // To store temp value of list2, 
            // I used add method.  Because ArrayList is an object type so if I assign 
            // list2 to temp1 then it will assign memory address rather 
            // than values.  Thus I will lose the values after invoking ascending() as 
            // all elements of list2 will shipped to list1.  So List2 becomes empty.
            {
                temp1.add(list2.get(i));
            }
            ascending(list2, list1);

            fixedPoint(list2, list1, temp1);
        }

    }

Answer 1

Purpose of writing this codes is that when all numbers are in ascending order then should stop calling a method called ascending(list2, list1)

然后您应该添加一个循环来检查 list1 的元素是否按升序排列，如下所示:

public void fixedPoint(ArrayList<Integer> list1, ArrayList<Integer> list2)
{
    boolean isAscending = true;
    for (int i = 1 ; (isAscending) && (i < list2.size()) ; i++) {
        isAscending = list2.get(i-1) < list2.get(i);
    }
    if (isAscending) {
        ... // Insert code to copy the data from list2 to list1.
        ... // Note that a simple assignment is not going to work here!
        System.out.println("found!!!");
        return;
    }
    // It's not in ascending order - continue recursing down.
    ascending(list2, list1);
    ArrayList<Integer> temp1 = new ArrayList<Integer>(list1); // store processed value
    fixedPoint(list2, list1);
    // temp1 makes the old value of list1 available for comparison
    System.out.println("st list1 is "+list1);
    System.out.println("st list1 was "+temp1);
    System.out.println("st list2 is "+list2);
}