package leetcode;

//206-单链表反转 https://leetcode-cn.com/problems/reverse-linked-list/

//遍历法

public class Solution1 {

private static ListNode copyNode(ListNode node){

return new ListNode(node.val);

}

//遍历法思路：从头遍历老链表 根据老元素复制出新元素，然后每复制出一个元素都插入新链表的head与第一个元素之间

public static ListNode reverseList(ListNode head) {

ListNode newHead;

if(head == null || head.next ==null){

return head;

}else{

ListNode temp =head;

newHead = copyNode(head) ;//临时头节点

ListNode addNode ;

while (temp!=null){

addNode =copyNode(temp);

addNode.next =newHead.next;

newHead.next = addNode;

temp = temp.next;

}

}

return newHead.next;

}

public static void main(String[] args) {

ListNode head1 = new ListNode(1);

ListNode head2 = new ListNode(2);

ListNode head3 = new ListNode(3);

ListNode head4 = new ListNode(4);

ListNode head5 = new ListNode(5);

ListNode head6 = new ListNode(6);

head1.next = head2;

head2.next = head3;

head3.next = head4;

head4.next = head5;

head5.next = head6;

list(head1);

ListNode newHead = reverseList(head1);

list(newHead);

}

private static void list(ListNode node){

while (node!=null){

System.out.print(node.val +"-");

node = node.next;

}

System.out.println();

}

}