【12_206】Reverse Linked List

本来没想出来，刚才突然想到，可以用“头插法”来反转

Reverse Linked List

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Question

Total Accepted: 66556 Total Submissions: 182891 Difficulty: Easy

Reverse a singly linked list.

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Discuss中的递归解法：

public ListNode reverseList(ListNode head) {
    return reverseListInt(head, null);
}

public ListNode reverseListInt(ListNode head, ListNode newHead) {
    if(head == null)
        return newHead;
    ListNode next = head.next;
    head.next = newHead;
    return reverseListInt(next, head);
}

我的代码：用的是迭代（即循环）的方法

C语言：

/**
 * 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* p = head->next;
    struct ListNode* q = p;
    head->next = NULL;
    while(p)    {
        p = p->next;
        q->next = head;
        head = q;
        q = p;
    }
    
    return head;
}