单链表、双链表及单链表的逆序

参考博客：数组、单链表和双链表介绍 以及 双向链表的C/C++/Java实现

              单向链表逆序

一、单链表

单链表结构如下图：

本文中，head节点也是包含数据的，并且最后一个节点指向的指针为NULL。

下图为单链表的删除操作：

下图为单链表的插入操作：

单链表的实现代码如下：

#ifndef SINGLE_LINK_H
#define SINGLE_LINK_H

#include <iostream>
using namespace std;

template<class T>
struct SNode
{
public:
    T data;
    SNode *next;
    SNode(){}
    SNode(T data, SNode *next)
    {
        this->data = data;
        this->next = next;
    }
};

template<class T>
class SingleLink
{
    public:
        SingleLink();
        ~SingleLink();

        SNode<T> *getHeadNode();
        void setHeadNode(SNode<T> *head);
        int getSize();
        bool isEmpty();
        T get(int index);
        T getFirst();
        T getLast();
        void insert(int index, T t);
        void insertFirst(T t);
        void appendLast(T t);
        void del(int index);
        void deleteFirst();
        void deleteLast();

    private:
        int count;
        SNode<T> *pHead;
        SNode<T> *getNode(int index);
};

template<class T>
SingleLink<T>::SingleLink() : count(0)
{
    pHead = new SNode<T>();
    pHead->next = NULL;
}

template<class T>
SingleLink<T>::~SingleLink()
{
    SNode<T> *ptmp;
    while(pHead->next != NULL)
    {
        ptmp = pHead;
        pHead = pHead->next;
        delete ptmp;
    }

    delete pHead;
    pHead = NULL;
}

template<class T>
int SingleLink<T>::getSize()
{
    return count;
}

template<class T>
bool SingleLink<T>::isEmpty()
{
    return count == 0;
}

template<class T>
SNode<T> *SingleLink<T>::getNode(int index)
{
    if(index < 0 || index >= count)
    {
        cout << "Get node failed! The index in out of bound!" << endl;
        return NULL;
    }

    SNode<T> *pindex = pHead;
    int i = 0;
    while(i++ < index)
    {
        pindex = pindex->next;
    }

    return pindex;
}

template<class T>
SNode<T> *SingleLink<T>::getHeadNode()
{
    return getNode(0);
}

template<class T>
void SingleLink<T>::setHeadNode(SNode<T> *head)
{
    this->pHead = head;
}

template<class T>
T SingleLink<T>::get(int index)
{
    return getNode(index)->data;
}

template<class T>
T SingleLink<T>::getFirst()
{
    return getNode(0)->data;
}

template<class T>
T SingleLink<T>::getLast()
{
    return getNode(count - 1)->data;
}

template<class T>
void SingleLink<T>::insert(int index, T t)
{
    SNode<T> *pnode;

    if(index == 0)
    {
        insertFirst(t);
    }
    else if(index == count)
    {
        appendLast(t);
    }
    else
    {
        SNode<T> *pindex = getNode(index - 1);
        pnode = new SNode<T>(t, pindex->next);
        pnode->data = t;
        pindex->next = pnode;
        count++;
    }
}

template<class T>
void SingleLink<T>::insertFirst(T t)
{
    if(count == 0)
    {
        pHead->data = t;
    }
    else
    {
        SNode<T> *pnode = new SNode<T>(t, pHead);
        pHead = pnode;
    }
    count++;
}

template<class T>
void SingleLink<T>::appendLast(T t)
{
    SNode<T> *pindex = getNode(count - 1);
    SNode<T> *pnode = new SNode<T>();
    pindex->next = pnode;
    pnode->data = t;
    pnode->next = NULL;
    count++;
}

template<class T>
void SingleLink<T>::del(int index)
{
    if(index >= count)
    {
        cout << "The index in out of bound!" << endl;
    }
    else
    {
        SNode<T> *pindex = getNode(index - 1);
        SNode<T> *ptmp = pindex->next;
        pindex->next = pindex->next->next;
        delete ptmp;
        ptmp = NULL;
        count--;
    }
}

template<class T>
void SingleLink<T>::deleteFirst()
{
    if(count == 0)
    {
        cout << "This single link is null!";
        return;
    }
    SNode<T> *ptmp = pHead;
    pHead = pHead->next;
    delete ptmp;
    ptmp = NULL;
    count--;
}

template<class T>
void SingleLink<T>::deleteLast()
{
    del(count - 1);
}

#endif

测试代码如下：

#include <iostream>
#include <string>
#include "DoubleLink.h"
#include "SingleLink.h"
using namespace std;

void IntTest()
{
    cout << "
----IntTest----" << endl;

    SingleLink<int> *pdlink = new SingleLink<int>();

    pdlink->insert(0, 20);
    pdlink->appendLast(10);
    pdlink->insertFirst(30);

    cout << "isEmpty() = " << pdlink->isEmpty() << endl;

    cout << "size() = " << pdlink->getSize() << endl;

    int sz = pdlink->getSize();
    for(int i = 0; i < sz; i++)
    {
        cout << "pdlink(" << i << ") = " << pdlink->get(i) << endl;
    }

    delete pdlink;
}

void StringTest()
{
    cout << "
----StringTest----" << endl;

    string sarr[3] = {"ten", "twenty", "thirty"};

    SingleLink<string> *pdlink = new SingleLink<string>();

    pdlink->insert(0, sarr[0]);
    pdlink->appendLast(sarr[1]);
    pdlink->insertFirst(sarr[2]);

    cout << "isEmpty() = " << pdlink->isEmpty() << endl;

    cout << "size() = " << pdlink->getSize() << endl;

    int sz = pdlink->getSize();
    for(int i = 0; i < sz; i++)
    {
        cout << "pdlink(" << i << ") = " << pdlink->get(i) <<endl;
    }

    delete pdlink;
}

struct stu
{
    int id;
    char name[20];
};

static stu arr_stu[] =
{
    {10, "sky"},
    {20, "jody"},
    {30, "vic"},
};

void ObjectTest()
{
    cout << "
----ObjectTest----" << endl;

    SingleLink<stu> *pdlink = new SingleLink<stu>();

    pdlink->insert(0, arr_stu[0]);
    pdlink->appendLast(arr_stu[1]);
    pdlink->insertFirst(arr_stu[2]);

    cout << "isEmpty() = " << pdlink->isEmpty() << endl;

    cout << "size() = " << pdlink->getSize() << endl;

    int sz = pdlink->getSize();
    struct stu p;
    for(int i = 0; i < sz; i++)
    {
        p = pdlink->get(i);
        cout << "pdlink(" << i << ") = [" << p.id << ", " << p.name << "]" << endl;
    }

    delete pdlink;
}

int main()
{
    IntTest();
    StringTest();
    ObjectTest();

    return 0;
}

二、双链表

双链表的结构如下：

本文的实现中，head节点作为一个特殊节点，不存储数据。

下图为双链表的删除操作：

下图为双链表的插入操作：

双链表的实现代码如下：

#ifndef DOUBLE_LINK_H
#define DOUBLE_LINK_H

#include <iostream>
using namespace std;

template<class T>
struct DNode
{
    public:
        T value;
        DNode *prev;
        DNode *next;
    public:
        DNode(){}
        DNode(T t, DNode *prev, DNode *next)
        {
            this->value = t;
            this->prev  = prev;
            this->next  = next;
        }
};

template<class T>
class DoubleLink
{
    public:
        DoubleLink();
        ~DoubleLink();

        int getSize();
        int isEmpty();

        T get(int index);
        T getFirst();
        T getLast();

        int insert(int index, T t);
        int insertFirst(T t);
        int appendLast(T t);

        int del(int index);
        int deleteFirst();
        int deleteLast();

    private:
        int count;
        DNode<T> *pHead;
    private:
        DNode<T> *getNode(int index);
};

template<class T>
DoubleLink<T>::DoubleLink() : count(0)
{
    pHead = new DNode<T>();
    pHead->prev = pHead->next = pHead;
    //count = 0;
}

template<class T>
DoubleLink<T>::~DoubleLink()
{
    DNode<T> *ptmp;
    DNode<T> *pnode = pHead->next;
    while(pnode != pHead)
    {
        ptmp = pnode;
        pnode = pnode->next;
        delete ptmp;
    }

    delete pHead;
    pHead = NULL;
}

template<class T>
int DoubleLink<T>::getSize()
{
    return count;
}

template<class T>
int DoubleLink<T>::isEmpty()
{
    return count == 0;
}

template<class T>
DNode<T> *DoubleLink<T>::getNode(int index)
{
    if(index < 0 || index >= count)
    {
        cout << "Get node failed! The index in out of bound!" << endl;
        return NULL;
    }

    if(index <= count/2)
    {
        int i = 0;
        DNode<T> *pindex = pHead->next;
        while(i++ < index)
        {
            pindex = pindex->next;
        }

        return pindex;
    }

    int j = 0;
    int lindex = count - index -1;
    DNode<T> *prindex = pHead->prev;
    while(j++ < lindex)
    {
        prindex = prindex->prev;
    }

    return prindex;
}

template<class T>
T DoubleLink<T>::get(int index)
{
    return getNode(index)->value;
}

template<class T>
T DoubleLink<T>::getFirst()
{
    return getNode(0)->value;
}

template<class T>
T DoubleLink<T>::getLast()
{
    return getNode(count - 1)->value;
}

template<class T>
int DoubleLink<T>::insert(int index, T t)
{
    if(index == 0)
    {
        return insertFirst(t);
    }

    DNode<T> *pindex = getNode(index);
    DNode<T> *pnode  = new DNode<T>(t, pindex->prev, pindex);
    pindex->prev->next = pnode;
    pindex->prev = pnode;
    count++;

    return 0;
}

template<class T>
int DoubleLink<T>::insertFirst(T t)
{
    DNode<T> *pnode   = new DNode<T>(t, pHead, pHead->next);
    pHead->next->prev = pnode;
    pHead->next = pnode;
    count++;

    return 0;
}

template<class T>
int DoubleLink<T>::appendLast(T t)
{
    DNode<T> *pnode   = new DNode<T>(t, pHead->prev, pHead);
    pHead->prev->next = pnode;
    pHead->prev = pnode;
    count++;

    return 0;
}

template<class T>
int DoubleLink<T>::del(int index)
{
    DNode<T> *pindex   = getNode(index);
    pindex->next->prev = pindex->prev;
    pindex->prev->next = pindex->next;
    delete pindex;
    count--;

    return 0;
}

template<class T>
int DoubleLink<T>::deleteFirst()
{
    DNode<T> *temp = pHead;
    pHead->next->prev = pHead->prev;
    pHead->prev->next = pHead->next;
    pHead = pHead->next;
    count--;
    delete temp;

    return 0;
}

template<class T>
int DoubleLink<T>::deleteLast()
{
    return del(count-1);
}

#endif

测试代码如下：

#include <iostream>
#include <string>
#include "DoubleLink.h"
#include "SingleLink.h"
using namespace std;

void IntTest()
{
    cout << "
----IntTest----" << endl;

    DoubleLink<int> *pdlink = new DoubleLink<int>();

    pdlink->insert(0, 20);
    pdlink->appendLast(10);
    pdlink->insertFirst(30);

    cout << "isEmpty() = " << pdlink->isEmpty() << endl;

    cout << "size() = " << pdlink->getSize() << endl;

    int sz = pdlink->getSize();
    for(int i = 0; i < sz; i++)
    {
        cout << "pdlink(" << i << ") = " << pdlink->get(i) << endl;
    }

    delete pdlink;
}

void StringTest()
{
    cout << "
----StringTest----" << endl;

    string sarr[3] = {"ten", "twenty", "thirty"};

    DoubleLink<string> *pdlink = new DoubleLink<string>();

    pdlink->insert(0, sarr[0]);
    pdlink->appendLast(sarr[1]);
    pdlink->insertFirst(sarr[2]);

    cout << "isEmpty() = " << pdlink->isEmpty() << endl;

    cout << "size() = " << pdlink->getSize() << endl;

    int sz = pdlink->getSize();
    for(int i = 0; i < sz; i++)
    {
        cout << "pdlink(" << i << ") = " << pdlink->get(i) <<endl;
    }

    delete pdlink;
}

struct stu
{
    int id;
    char name[20];
};

static stu arr_stu[] =
{
    {10, "sky"},
    {20, "jody"},
    {30, "vic"},
};

void ObjectTest()
{
    cout << "
----ObjectTest----" << endl;

    DoubleLink<stu> *pdlink = new DoubleLink<stu>();

    pdlink->insert(0, arr_stu[0]);
    pdlink->appendLast(arr_stu[1]);
    pdlink->insertFirst(arr_stu[2]);

    cout << "isEmpty() = " << pdlink->isEmpty() << endl;

    cout << "size() = " << pdlink->getSize() << endl;

    int sz = pdlink->getSize();
    struct stu p;
    for(int i = 0; i < sz; i++)
    {
        p = pdlink->get(i);
        cout << "pdlink(" << i << ") = [" << p.id << ", " << p.name << "]" << endl;
    }

    delete pdlink;
}

int main()
{
    IntTest();
    StringTest();
    ObjectTest();

    return 0;
}

两种链表的测试结果相同，都为：

----IntTest----
isEmpty() = 0
size() = 3
pdlink(0) = 30
pdlink(1) = 20
pdlink(2) = 10

----StringTest----
isEmpty() = 0
size() = 3
pdlink(0) = thirty
pdlink(1) = ten
pdlink(2) = twenty

----ObjectTest----
isEmpty() = 0
size() = 3
pdlink(0) = [30, vic]
pdlink(1) = [10, sky]
pdlink(2) = [20, jody]

三、单向链表的逆序

1、循环逆序

代码如下：

#include <iostream>
#include <string>
#include "DoubleLink.h"
#include "SingleLink.h"
using namespace std;

int main()
{
    cout << "
----ReverseTest----" << endl;

    SingleLink<int> *pdlink = new SingleLink<int>();

    pdlink->insert(0, 1);
    pdlink->insert(0, 2);
    pdlink->insert(0, 3);
    pdlink->insert(0, 4);
    pdlink->insert(0, 5);

    cout << "
----Before reverse----" << endl;
    cout << "size() = " << pdlink->getSize() << endl;
    int sz = pdlink->getSize();
    for(int i = 0; i < sz; i++)
    {
        cout << "pdlink(" << i << ") = " << pdlink->get(i) << endl;
    }

     SNode<int> *current = pdlink->getHeadNode();
     SNode<int> *next = NULL, *result = NULL;
     while(current != NULL)
     {
         next = current->next;
         current->next = result;
         result = current;
         current = next;
     }
     pdlink->setHeadNode(result);

     cout << "
----After reverse----" << endl;
     for(int i = 0; i < sz; i++)
     {
         cout << "pdlink(" << i << ") = " << pdlink->get(i) << endl;
     }

     delete pdlink;

     return 0;
}

根据上面代码的思路，下图以1——>2——>3——>NULL这个链表为例，用图示来说明逆序的过程：

2、递归逆序

代码如下：

#include <iostream>
#include <string>
#include "DoubleLink.h"
#include "SingleLink.h"
using namespace std;

template<class T>
SNode<T> *ReverseSingleLink(SNode<T> *phead)
{
    SNode<T> *newHead;
    if(phead->next == NULL) return phead;
    newHead = ReverseSingleLink(phead->next);

    phead->next->next = phead;
    phead->next = NULL;

    return newHead;
}

int main()
{
    cout << "
----ReverseTest----" << endl;

    SingleLink<int> *pdlink = new SingleLink<int>();

    pdlink->insert(0, 1);
    pdlink->insert(0, 2);
    pdlink->insert(0, 3);
    pdlink->insert(0, 4);
    pdlink->insert(0, 5);

    cout << "
----Before reverse----" << endl;
    cout << "size() = " << pdlink->getSize() << endl;
    int sz = pdlink->getSize();
    for(int i = 0; i < sz; i++)
    {
        cout << "pdlink(" << i << ") = " << pdlink->get(i) << endl;
    }

    pdlink->setHeadNode(ReverseSingleLink(pdlink->getHeadNode()));
    cout << "
----After reverse----" << endl;
    cout << "size() = " << pdlink->getSize() << endl;
    for(int i = 0; i < sz; i++)
    {
        cout << "pdlink(" << i << ") = " << pdlink->get(i) << endl;
    }

    delete pdlink;

    return 0;
}

两种逆序算法的结果都为：

----ReverseTest----

----Before reverse----
size() = 5
pdlink(0) = 5
pdlink(1) = 4
pdlink(2) = 3
pdlink(3) = 2
pdlink(4) = 1

----After reverse----
size() = 5
pdlink(0) = 1
pdlink(1) = 2
pdlink(2) = 3
pdlink(3) = 4
pdlink(4) = 5