zoukankan      html  css  js  c++  java
  • Leetcode--Reverse Nodes in k-Group

    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

    分析:看到这个题目第一想法就是就地操作,依次以k个元素为一组来逆置,最后少于k个元素的组不逆置,可是实际操作时将前后两组的首尾相连不是非常好操作,于是直接利用栈将k个元素进栈出栈实现逆置,详细实现时先统计出链表的总元素个数,提前算出须要逆置的组数,代码例如以下:

    /**
     * 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;
        }
    };


  • 相关阅读:
    Android ListView的使用(三)
    Android GridView的使用页面按钮
    Android ListView的使用(二)
    Android ListView的使用(一)
    Linux 下MongoDb的安装
    Linux使用redis
    JavaWeb之JDBC
    JavaWeb之多语言国际化
    JavaWeb之JSTL标签
    JavaWeb之JSP技术总结
  • 原文地址:https://www.cnblogs.com/bhlsheji/p/4093586.html
Copyright © 2011-2022 走看看