LeetCode 206. Reverse Linked List

Reverse a singly linked list.

/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* reverseList(ListNode* head) {
ListNode *pre = NULL;
while (head != NULL) {
ListNode *cur = head;
head = head->next;
cur->next = pre;
pre = cur;
}
return pre;
}
};

/** Recursion
* class Solution {
* public:
* ListNode* reverseList(ListNode* head) {
* if ((head == NULL) || (head->next == NULL)) {
* return head;
* }
* ListNode *rest = reverseList(head->next);
* head->next->next = head;
* head->next = NULL;
* return rest;
* }
* };
*/