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  • [LeetCode]Reverse Linked List II

    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.

    /**
     * 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) {
            ListNode *p=head;
            ListNode *newhead=NULL,*first,*cur=NULL,*last;
            int count=1;
            if(m==1) //翻转头结点
            {
                newhead=first=p;
                while(p)
                {
                    if(count==n) return newhead;
                    p=p->next;count++;
                    first->next=p->next;
                    p->next=newhead;
                    newhead=p;
                    p=first;
                }
            }
            else
            {
                newhead=head;
                while(p)
                {
                    if(count+1==m) 
    				{
    					cur=p;
    					first=cur->next;
    				}
                    p=p->next;count++;
                    if(cur&&count<=n)
                    {
    					last=cur->next;
    					if(p!=first)
    					{
    						cur->next=p;
    						first->next=p->next;
    						p->next=last;
    						p=first;
    					}
                    }
                }
    			return newhead;
            }
    		return newhead;
        }
    };
    

      

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  • 原文地址:https://www.cnblogs.com/Rosanna/p/3522353.html
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