[英]Java recursive method end but doesn't terminate
我正在编写一种用于双向链接列表数据结构的方法,该方法应该按照参数中的指定将索引从索引a到b的元素列表反转,并决定以递归方式进行操作。 分配的目的是练习使用节点的指针操纵。 我的方法的逻辑对我来说似乎还可以,但是当我通过JUnit测试运行代码时,它不会结束。 考虑到这很奇怪,我添加了println语句来查看它到达了代码的哪一部分; 一切都检查完了。 因此,我在Eclipse的调试器中运行了它,并在经过所有递归调用后一直返回到结束括号,而没有终止。 它只是放在尾端,而我之前从未见过这样的东西。 为什么这样做,我该怎么做才能解决?
这是代码:
public void reverseList(int start, int end)
{
if (start >= end)
{
return;
}
ListNode left = getListNode(start);
ListNode right = getListNode(end);
ListNode leftNext = left.next;
ListNode leftPrev = left.previous;
ListNode rightNext = right.next;
ListNode rightPrev = right.previous;
leftPrev.next = right;
rightPrev.next = left;
leftNext.previous = right;
rightNext.previous = left;
left.next = rightNext;
left.previous = rightPrev;
right.next = leftNext;
right.previous = leftPrev;
reverseList(start + 1, end - 1);
}
编辑:这是测试它的代码
JUnit:
@Test
public void testReveseList()
{
StudentList list = new StudentList();
list.add("a", "");
list.add("b", "");
list.add("c", "");
list.add("d", "");
list.add("e", "");
list.add("f", "");
list.add("g", "");
list.add("h", "");
list.add("i", "");
list.add("j", "");
list.printlist();
list.reverseList(2, 5);
System.out.println();
StudentList expectedList = new StudentList();
expectedList.add("a", "");
expectedList.add("b", "");
expectedList.add("f", "");
expectedList.add("e", "");
expectedList.add("d", "");
expectedList.add("c", "");
expectedList.add("g", "");
expectedList.add("h", "");
expectedList.add("i", "");
expectedList.add("j", "");
assertEquals(expectedList, list);
list.reverseList(2, 5);
System.out.println();
StudentList expectedList1 = new StudentList();
expectedList1.add("a", "");
expectedList1.add("b", "");
expectedList1.add("c", "");
expectedList1.add("d", "");
expectedList1.add("e", "");
expectedList1.add("f", "");
expectedList1.add("g", "");
expectedList1.add("h", "");
expectedList1.add("i", "");
expectedList1.add("j", "");
assertEquals(expectedList1, list);
list.reverseList(0, 9);
System.out.println();
StudentList expectedList2 = new StudentList();
expectedList2.add("j", "");
expectedList2.add("i", "");
expectedList2.add("h", "");
expectedList2.add("g", "");
expectedList2.add("f", "");
expectedList2.add("e", "");
expectedList2.add("d", "");
expectedList2.add("c", "");
expectedList2.add("b", "");
expectedList2.add("a", "");
assertEquals(expectedList2, list);
}
测试类别:
public class StudentList
{
private ListNode head = null;
public void add(StudentData data)
{
ListNode newNode = new ListNode(data);
ListNode lastNode = getTail();
if (lastNode == null)
{
head = newNode;
}
else
{
lastNode.next = newNode;
}
newNode.previous = lastNode;
newNode.next = null;
}
public ListNode getListNode(int indexOfDesiredNode)
{
if (indexOfDesiredNode >= size())
{
// --- Error: There aren't that many nodes
return null;
}
// --- Move through the list, node by node, until we find
// --- the one we want
int count = 0;
ListNode current = head;
while ((count < indexOfDesiredNode) && (null != current))
{
current = current.next;
count = count + 1;
}
// --- So, did we find anything?
if (null == current)
{
// --- Error: We didn't find the node
return null;
}
return current;
}
public int size()
{
if (null == head)
{
return 0;
}
int count = 0;
ListNode current = head;
while (current != null)
{
count = count + 1;
current = current.next;
}
return count;
}
public void reverseList(int start, int end)
{
if (start >= end)
{
return;
}
ListNode left = getListNode(start);
ListNode right = getListNode(end);
ListNode leftNext = left.next;
ListNode leftPrev = left.previous;
ListNode rightNext = right.next;
ListNode rightPrev = right.previous;
leftPrev.next = right;
rightPrev.next = left;
leftNext.previous = right;
rightNext.previous = left;
left.next = rightNext;
left.previous = rightPrev;
right.next = leftNext;
right.previous = leftPrev;
//-- The easy way of doing it... *sigh*
// StudentData temp = get(start);
// getListNode(start).data = getListNode(end).data;
// getListNode(end).data = temp;
reverseList(start + 1, end - 1);
}
}
和ListNode类:
public class ListNode
{
public StudentData data = null;
public ListNode next = null;
public ListNode previous = null;
public ListNode(StudentData data)
{
this.data = data;
}
@Override
public String toString()
{
return data.toString();
}
}
抱歉,复制和粘贴时格式不是最好的。
问题在于end == start + 1
,因此rightPrev == left
。 然后,您设置rightPrev.next = left
可使列表循环,因此getListNode
不会终止。
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