[LeetCode]Reverse Linked List

最新推荐文章于 2020-03-28 23:36:09 发布

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本文介绍了一种使用迭代和递归两种方法实现单链表反转的技术。通过实例代码展示了如何找到链表各节点之间的正确关系，并提供了详细的递归实现步骤。

Reverse a singly linked list.

click to show more hints.

Hint:

A linked list can be reversed either iteratively or recursively. Could you implement both?

非递归：找好链表关系不难解决：

/**
 * 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)
            return NULL;
        ListNode* pre = new ListNode(-1);
        pre->next = head;
        ListNode* cur = head;
        ListNode* nex = head;
        while(cur->next){
            nex = cur->next;
            cur->next = nex->next;
            nex->next = pre->next;
            pre->next = nex;
        }
        return pre->next;
    }
};

递归：递归地把后一个元素放到前一个元素前面。

class Solution {
public:
    ListNode *reverseList(ListNode *head) {
        return f(head, NULL);
    }

    ListNode *f(ListNode *cur, ListNode *pre){
        if(not cur)
            return pre;
        ListNode *post = cur->next;
        cur->next = pre;
        return f(post, cur);
    }
};