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  • 链表//反转链表

    反转一个单链表。

    示例:

    输入: 1->2->3->4->5->NULL
    输出: 5->4->3->2->1->NULL

    进阶:
    你可以迭代或递归地反转链表。你能否用两种方法解决这道题?

    递归:

    /**
     * Definition for singly-linked list.
     * public class ListNode {
     *     int val;
     *     ListNode next;
     *     ListNode(int x) { val = x; }
     * }
     */
    class Solution {
        public ListNode reverseList(ListNode head) {
            if(head==null||head.next==null)
                return head;
            ListNode h = reverseList(head.next);
            head.next.next = head;
            head.next = null;
            return h;
        }
    }
    /**
     * 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) {
            if(head==NULL||head->next==NULL)
                return head;
            ListNode *h = reverseList(head->next);
            head->next->next = head;
            head->next = NULL;
            return h;
        }
    };

    迭代:

    /**
     * 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) {
            if(head == NULL || head->next == NULL)
                return head;
            ListNode *p = head;
            ListNode *q = head->next;
            ListNode *r = head->next->next;
            p->next = NULL;
            while(r != NULL){
                q->next = p;
                p = q;
                q = r;
                r = r->next;
            }
            q->next = p;
            return q;
        }
    };
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  • 原文地址:https://www.cnblogs.com/strawqqhat/p/10602311.html
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