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 returnif(head == null) {return newHead;}Node temp = head.next;head.next = newHead; //this will initially be nullnewHead = 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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