【LeetCode】206. 反转链表—力扣

        给你单链表的头节点 head ，请你反转链表，并返回反转后的链表。

206. 反转链表 - 力扣（Leetcode）

 

 

 方法一：

         就是不断头插，用头插法！

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */
 
 
struct ListNode* reverseList(struct ListNode* head){
    struct ListNode* newhead = NULL;
    struct ListNode* cur = head;
    struct ListNode* next = NULL;
    while(cur)
    {
        next = cur->next;
        cur->next = newhead;
        newhead = cur;
        cur = next;
    }
    return newhead;
}

方法二：

        改一下指针方向

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */
 
 
struct ListNode* reverseList(struct ListNode* head){
    if(head == NULL)
    {
        return NULL;
    }
    struct ListNode* n1,*n2, *n3;
    n1 = NULL;
    n2 = head;
    n3 = n2->next;
    while(n2)
    {
        n2->next = n1;
        n1 = n2;
        n2 = n3;
        if(n3)
            n3 = n3->next; 
    }
    return n1;
}