LeetCode 206 Reverse Linked List

LeetCode  206 Reverse Linked List

递归：

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

迭代：

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