14--反转链表

//
//  main.cpp
//  test_list_oper
//
//  Created by Hugo Cao  on 15/7/6.
//  Copyright (c) 2015年 Hugo Cao . All rights reserved.
//

/*
题目：反转链表
    伴随着大量的指针操作，3个指针，复杂度O(n).
//反转链表，三个指针，遍历一次。
lNode * secondReseverList(lNode *head)
{
    //如果链表长度为0或者1，那么不需要翻转
    if (head == NULL || head->m_pNext == NULL)
    {
        cout << "无需翻转" << endl;
        return head;
    }
    
    lNode *p_head = NULL;   //返回的头节点
    lNode *p_Node = head;   //当前结点
    lNode *p_Prev = NULL;   //前一个节点
    
    while (p_Node != NULL)
    {
        //下一个节点,这是很关键的一步
        lNode *p_Next = p_Node->m_pNext;      
        if (p_Next == NULL)
        {
            p_head = p_Node;
        }
        
        p_Node->m_pNext = p_Prev;
        p_Prev = p_Node;
        p_Node = p_Next;

    }
    
    return p_head;
}
*/

#include <stdio.h>
#include <stdlib.h>
#include <stack>
#include <iostream>
using namespace std;

typedef struct ListNode
{
    int m_nValue;
    struct ListNode *m_pNext;
} lNode;


//添加元素结点
void listAddNode(lNode *head)
{
    lNode *p = head, *p_Inter = NULL;
    
    if (!(p_Inter = ((lNode *)malloc(sizeof(lNode)))))
    {
        printf("the memery is don't create it\n");
        return;
    }
    p_Inter->m_pNext = NULL;
    
    int data;
    printf("请输入数字：\n");
    scanf("%d", &data);
    p_Inter->m_nValue = data;
    
    while (p->m_pNext != NULL)
    {
        p = p->m_pNext;
    }
    
    p->m_pNext = p_Inter;
    
}


//创建元素结点
lNode* createList(lNode *head)
{
    if (!(head = ((lNode *)malloc(sizeof(lNode)))))
    {
        printf("the memery is don't create it\n");
        return NULL;
    }
    head->m_pNext = NULL;
    int data;
    printf("请输入数字：\n");
    scanf("%d", &data);
    head->m_nValue = data;
    
    
    lNode *p = head;
    char X_cin = 'Y';
    while (true)
    {
        printf("是否继续添加:N/n \n");
        cin >> X_cin;
        
        if (X_cin == 'y' || X_cin == 'Y')
        {
            ;
        }
        else if (X_cin == 'N' || X_cin == 'n')
        {
            return head;
        }
        else
        {
            ;
        }
        
        listAddNode(p);
    }
    
}


//显示列表
void showList(lNode *head)
{
    if (NULL == head)
    {
        cout << "list is empty \n" << endl;
        return;
    }
    
    lNode *p = head;
    
    while (p != NULL)
    {
        printf("%d\n", p->m_nValue);
        p = p->m_pNext;
    }
    
}


//翻转链表
void reversePut(lNode *point)
{
    stack <int> stack_rev;
    lNode *p = point;
    
    while (p != NULL)
    {
        stack_rev.push(p->m_nValue);
        p = p->m_pNext;
    }
    
    cout << "翻转以后的输出" << endl;
    while (!stack_rev.empty())
    {
        cout << stack_rev.top() << endl;
        stack_rev.pop();
    }
}


//输出倒数第K个元素节点，遍历所有节点型。
void firstPrintNode(lNode *head, int kNum)
{
    int length = 0;
    lNode *p = head;
    
    while (p != NULL) {
        p = p->m_pNext;
        length++;
    }
    if (length < kNum)
    {
        cout << "链表长度为：" << length << ", 而遍历的节点位置是： "<< kNum << endl;
        return;
    }
    cout << "链表长度为：" << length;
    p = head;
    while (length != kNum) {
        length--;
        p =  p->m_pNext;
    }
    
    cout << "  输出倒数第K个元素节点: " << p->m_nValue << endl;
}

//输出第K个结点，第二种方式，两个指针
void secondPrintNode(lNode *head, int kNum)
{
    lNode *p1 = head;
    lNode *p2 = head;
    int length = kNum;
    
    while (p1 != NULL) {
        p1 = p1->m_pNext;
        length--;
        if (length < 0)
            p2 = p2->m_pNext;
    }
    
    cout << "  输出倒数第K个元素节点: " << p2->m_nValue << endl;
}

//反转链表，三个指针，遍历一次。
lNode * secondReseverList(lNode *head)
{
    //如果链表长度为0或者1，那么不需要翻转
    if (head == NULL || head->m_pNext == NULL)
    {
        cout << "无需翻转" << endl;
        return head;
    }
    
    lNode *p_head = NULL;   //返回的头节点
    lNode *p_Node = head;   //当前结点
    lNode *p_Prev = NULL;   //前一个节点
    
    while (p_Node != NULL)
    {
        lNode *p_Next = p_Node->m_pNext;      //下一个节点
        if (p_Next == NULL)
        {
            p_head = p_Node;
        }
        
        p_Node->m_pNext = p_Prev;
        p_Prev = p_Node;
        p_Node = p_Next;

    }
    
    return p_head;
}


int main()
{
    lNode *head = NULL;
    
    head = createList(head);
    //showList(head);
    //翻转链表，用栈实现，
    //reversePut(head);
    //输出倒数第K个元素
    //secondPrintNode(head, 3);
    //secondReseverList(head);
    head = secondReseverList(head);
    showList(head);
    return 0;
}