lintcode 翻转链表
描述
翻转一个链表
样例
给出一个链表1->2->3->null,这个翻转后的链表为3->2->1->null
挑战
在原地一次翻转完成
思路
在原地反转,那么就是一边迭代一边跟新每个节点的next指针,把当前节点cur 指向cur->next->next 他的下一个节点指向head,最后跟新一下节点的信息。返回head。因为涉及到了4个 head cur cur->next cur->next->next 所以退出循环的条件是cur->next == null
/**
* Definition of singly-linked-list:
*
* class ListNode {
* public:
* int val;
* ListNode *next;
* ListNode(int val) {
* this->val = val;
* this->next = NULL;
* }
* }
*/
class Solution {
public:
/**
* @param head: n
* @return: The new head of reversed linked list.
*/
ListNode * reverse(ListNode * head) {
// write your code here
if (!head || !head->next)
return head;
if (!head->next->next) {
ListNode *cur = head->next;
cur ->next = head;
head ->next = NULL;
return cur;
}
ListNode *cur = head -> next;
ListNode *temp = cur -> next;
cur->next = head;
head->next = temp;
head = cur;
cur = head->next;
while (cur->next){
temp = cur->next;
cur ->next = cur->next->next;
temp->next = head;
head = temp;
}
return head;
}
};