Leetcode--Reverse Nodes in k-Group

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Problem Description:

Given a linked list, reverse the nodes of a linked list k at a time and return its modified list.

If the number of nodes is not a multiple of k then left-out nodes in the end should remain as it is.

You may not alter the values in the nodes, only nodes itself may be changed.

Only constant memory is allowed.

For example,
Given this linked list: 1->2->3->4->5

For k = 2, you should return: 2->1->4->3->5

For k = 3, you should return: 3->2->1->4->5

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *reverseKGroup(ListNode *head, int k) {
        ListNode *p=head,*newh=NULL,*pre; 
		stack<ListNode *> stk;
        int len=0,i=1,cnt,n;
        while(p)
        {
            len++;
            p=p->next;
        }
        if(k>len||k<=1)
            return head;
        n=len/k;
        p=head;
        while(i<=n)
        {
            cnt=0;
			while(cnt<k)
			{
				stk.push(p);
				p=p->next;
				cnt++;
			}
			while(!stk.empty())
			{
				if(!newh)
				{
					newh=stk.top();
					pre=newh;
					stk.pop();
				}
				else
				{
					pre->next=stk.top();
					pre=pre->next;
					stk.pop();
				}
			}            
            i++;
        }
        pre->next=p;
        return newh;
    }
};

Leetcode--Reverse Nodes in k-Group,布布扣,bubuko.com

Leetcode--Reverse Nodes in k-Group

标签：des   style   color   os   for   io   

原文地址：http://blog.csdn.net/longhopefor/article/details/37695801