题目描述
输入一个链表,反转链表后,输出新链表的表头。
栈法:
/*
public class ListNode {
int val;
ListNode next = null;
ListNode(int val) {
this.val = val;
}
}*/
import java.util.Stack;
public class Solution {
public ListNode ReverseList(ListNode head) {
if(head==null)
return null;
Stack <ListNode> stack=new Stack();
while(head.next!=null){
stack.push(head);
head=head.next;
}
ListNode temp=head;
while(!stack.isEmpty()){
temp.next=stack.pop();
temp=temp.next;
}
temp.next=null;
return head;
}
}
指针法:
/*
public class ListNode {
int val;
ListNode next = null;
ListNode(int val) {
this.val = val;
}
}*/
import java.util.Stack;
public class Solution {
public ListNode ReverseList(ListNode head) {
ListNode pre=null;
ListNode next=null;
while(head!=null){
next=head.next;
head.next=pre;
pre=head;
head=next;
}
return pre;
}
}