英文:
Reverse a linked list recursively in java using a temp variable
问题
我在Java中实现了一个反转链表的解决方案，这是我在网上找到的。但由于某种原因，在我的代码中它不起作用。
当我打印链表时，它只打印第一个节点。我知道打印方法有效，因为当我不尝试反转时，它会打印整个链表。
在这段代码中我哪里出错了？
public class LinkedLists {
public static void main(String[] args) {
LinkedList list = new LinkedList();
list.addLast(10);
list.addLast(20);
list.addLast(30);
list.reverseList();
list.print();
}
public static class LinkedList {
private class Node {
private int value;
private Node next;
}
public Node first;
public Node last;
public void addLast(int item) {
Node node = new Node();
node.value = item;
if (first == null) {
first = node;
last = node;
} else {
last.next = node;
last = node;
}
}
private Node reverse(Node head, Node newHead) {
if (head == null) {
return newHead;
}
Node temp = head.next;
head.next = newHead;
newHead = head;
head = temp;
return reverse(head, newHead);
}
public Node reverseList() {
return reverse(first, null);
}
public void print() {
Node current = first;
while (current != null) {
System.out.print(current.value + " ");
current = current.next;
}
}
} //class ends
}
英文:
I implemented a solution to reverse a linked list in java that I found online. But it is not working in my code for some reason.
When I print the list it only prints the first node. I know the print method works because it prints the whole thing when I don't try to reverse.
Where did I go wrong in this code?
public class LinkedLists {
public static void main(String[] args) {
LinkedList list = new LinkedList();
list.addLast(10);
list.addLast(20);
list.addLast(30);
list.reverseList();
list.print();
}
public static class LinkedList{
private class Node{
private int value;
private Node next;
}
public Node first;
public Node last;
public void addLast(int item){
Node node = new Node();
node.value = item;
if(first == null) {
first = node;
last = node;
} else {
last.next = node;
last = node;
}
}
private Node reverse(Node head, Node newHead) {
//base case: when first = last you return
if(head == null) {
return newHead;
}
Node temp = head.next;
head.next = newHead; //this will initially be null
newHead = head;
head = temp;
return reverse(head, newHead);
}
public Node reverseList() {
return reverse(first, null);
}
public void print(){
Node current = first;
while (current != null){
System.out.print(current.value + " ");
current = current.next;
}
}
} //class ends
}
答案1
得分: 2
虽然 reverse 返回了新头部的正确引用，但在主程序中初始调用 reverseList 的时候忽略了这个返回的引用。
你的 reverseList 方法最好不要返回任何内容，而是更新 first 和 last 成员：
public void reverseList() {
last = first;
first = reverse(first, null);
}
英文:
Although reverse returns the correct reference for the new head, the initial call of reverseList -- in the main program -- ignores this returned reference.
Your reverseList method should better not return anything, but instead update the first and last members:
public void reverseList() {
last = first;
first = reverse(first, null);
}
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