Reverse Linked List II

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本文介绍了一种反转链表中指定区间[m, n]的方法。通过使用辅助头结点简化边界条件处理，并详细展示了如何反转从第m个节点到第n个节点的过程。此算法适用于解决涉及链表区间操作的问题。

/**
 * 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(head==NULL || head->next==NULL)
            return head;
        ListNode *newHead = new ListNode(-1);
        newHead->next = head;
        ListNode* begin=head;
        ListNode* preBegin=newHead;
        ListNode* end=newHead;
        ListNode* postEnd=head;
        while(--m)
        {
            preBegin=preBegin->next;
            begin=begin->next;
        }
        
        while(n--)
        {
            postEnd=postEnd->next;
            end=end->next;
        }
        
        reverse(begin,end);
        preBegin->next=begin;
        end->next=postEnd;
        
        return newHead->next;
        
    }
    void reverse(ListNode*& begin, ListNode*& end)
    {
        if(begin == end)
            return;
        else if(begin->next == end)
            end->next = begin;
        else
        {//at least 3 nodes
            ListNode* pre = begin;
            ListNode* cur = pre->next;
            ListNode* post = cur->next;
            while(post != end->next)
            {
                cur->next = pre;
                pre = cur;
                cur = post;
                post = post->next;
            }
            cur->next = pre;
        }
        //swap
        ListNode* temp = begin;
        begin = end;
        end = temp;
    }
};