LeetCode-Reverse Linked List II

最新推荐文章于 2024-05-18 16:06:33 发布

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最新推荐文章于 2024-05-18 16:06:33 发布

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分类专栏： Cracking LeetCode List 文章标签： leetcode Reverse Linked List

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本文介绍了一种算法，用于在单次遍历中就地反转链表的指定区间，提供了完整的C++实现代码，并附带链表节点定义。适用于m到n范围内的节点，确保1≤ m ≤ n ≤ 链表长度。

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Reverse a linked list from position m to n. Do it in-place and in one-pass.

For example:
Given 1->2->3->4->5->NULL, m = 2 and n = 4,

return 1->4->3->2->5->NULL.

Note:
Given m, n satisfy the following condition:
1 ≤ m ≤ n ≤ length of list.

Solution:

Code:

<span style="font-size:14px;">/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *reverseBetween(ListNode *head, int m, int n) {
        if (m == n) return head;
        if (m == 1) {
            ListNode *begin = head, *end = head, *headNext; 
            head = head->next;
            for (int i = 0; i < n-m; i++) {
                headNext = head->next;
                head->next = begin;
                begin = head;
                head = headNext;
            }
            end->next = head;
            return begin;
        } else {
            ListNode *begin, *end, *left, *temp = head, *tempNext;
            for (int i = 2; i < m; i++)
                temp = temp->next;
            left = temp;
            temp = temp->next;
            begin = temp;
            end = temp;
            temp = temp->next;
            for (int i = 0; i < n-m; i++) {
                tempNext = temp->next;
                temp->next = begin;
                begin = temp;
                temp = tempNext;
            }
            left->next = begin;
            end->next = temp;
            return head;
        }
    }
};</span>