Leetcode Reverse Linked List

Reverse a singly linked list.

Hint:

A linked list can be reversed either iteratively or recursively. Could you implement both?

Java code:iteratively:

/*** Definition for singly-linked list. * public class ListNode {* int val; * ListNode Next; * ListNode (int X) {val = x;}}*/ Public classSolution { PublicListNode reverselist (ListNode head) {if(Head = =NULL|| Head.next = =NULL) {            returnHead; } listnode p1=Head; ListNode P2=Head.next; Head.next=NULL;  while(P1! =NULL&& P2! =NULL) {ListNode P3=P2.next; P2.next=P1; P1=P2; if(p3!=NULL) {P2=P3; }Else {                 Break; }        }        returnP2; }}

Recursively:

Version One:

  PublicListNode reverselist (ListNode head) {if(head==NULL|| Head.next = =NULL)        returnHead; //Get second nodeListNode second =Head.next; //set first ' next ' is nullHead.next =NULL; ListNode Rest=Reverselist (second); Second.next=Head; returnrest; }

Version two:

 Public ListNode reverselist (ListNode head) {        returnnull);    }      Public ListNode Reverselistint (ListNode head, ListNode newhead) {        ifnull)             return  newhead;         = Head.next;         = Newhead;         return Reverselistint (Next, head);    }

20160601:

Iteration:

 Public classSolution { PublicListNode reverselist (ListNode head) {//Iteration//Base Case        if(Head = =NULL|| Head.next = =NULL) {            returnHead; } ListNode Pre=NULL; ListNode cur=Head; ListNode Next=NULL;  while(cur! =NULL) {Next=Cur.next; Cur.next=Pre; Pre=cur; Cur=Next; }        returnPre; }}

Recursion:

 Public classSolution { PublicListNode reverselist (ListNode head) {//recursion//Base Case        if(Head = =NULL|| Head.next = =NULL) {            returnHead; } ListNode NextNode=Head.next; ListNode Newhead=reverselist (NextNode); Nextnode.next=Head; Head.next=NULL; returnNewhead; }}

Reference:

1. http://www.programcreek.com/2014/05/leetcode-reverse-linked-list-java/

2. Https://leetcode.com/discuss/34474/in-place-iterative-and-recursive-java-solution

Leetcode Reverse Linked List