[英]sort strings in alphabetical order with linked lists in c++
我正在分配链接的字符串列表。 一切正常,直到我进入排序部分。 我也在使用类。 我已经有2个功能。 第一个minimum(string)
,它返回按字母顺序排在最前面的字符串。
此功能工作正常。 我还有一个函数remove(string)
,它从链表中删除包含给定字符串的节点。 如果成功,则返回true,否则返回false(如果字符串不在列表中),在这种情况下,我必须擦除minimum(string)
函数返回的minimum(string)
。 我遇到的功能是sort()
。
它希望我将StringNode
指针定义为新列表(空列表)的头,然后需要一个循环,在该循环中我将调用minimum(string)
和remove(string)
函数。 在循环内部,我还需要将此节点插入新列表中的适当位置(将其追加到末尾)。 旧的头指针(现在为空)必须指向新列表。
我对此很困惑,到目前为止,我有:
void StringList::sort()
{
StringNode *newList = new StringNode;
newList = NULL;
string mini;
bool removed;
while (newList->next != NULL)
{
StringNode *newList2 = new StringNode;
StringNode *p = head;
mini = minimum();
p->data = mini;
p->next = NULL;
newList2 = newList2->next;
newList2->next = p;
removed = remove(mini);
newList = newList2;
}
}
我的理解是:我需要创建一个新节点,该节点将是一个空列表,意味着newList->next = NULL;
然后在循环上,我需要创建另一个新节点,以及一个指向循环内新节点头的指针。 我需要将最小值给出的值存储在指针p
,并使指针指向新节点。
任何帮助将不胜感激。 谢谢!
这是孔程序。
// StringList.cpp
#include <iomanip>
#include <iostream>
#include <sstream>
#include "StringList.h"
using namespace std;
//******************************************************************************
// StringList: creates an empty list
//******************************************************************************
StringList::StringList()
{
head = NULL;
}
//******************************************************************************
// StringList: deallocates all the nodes in StringList
//******************************************************************************
StringList::~StringList()
{
StringNode *p;
StringNode *n;
p = head;
while (p != NULL)
{
n = p->next;
delete p;
p = n;
}
}
//******************************************************************************
// count: returns the total number of nodes in the list.
//******************************************************************************
int StringList::count()
{
int count = 0;
StringNode *p;
p = head;
while ( p != NULL )
{
count++;
p = p->next;
}
return count;
}
//******************************************************************************
// add: adds a new node to the beginning of the list.
//******************************************************************************
void StringList::add(string movie)
{
StringNode *newNode = new StringNode;
newNode->data = movie;
newNode->next = head;
head = newNode;
}
//******************************************************************************
// remove: removes a node containing the string from linked list
// returns true if successful or false the string is not in the list
//******************************************************************************
bool StringList::remove(string movie)
{
StringNode *p = head;
StringNode *n = NULL;
while (p != NULL && p->data != movie )
{
n = p;
p = p->next;
if (p == NULL )
{
return false;
}
else if (p->data == movie)
{
n->next = p->next;
delete p;
return true;
}
}
}
//******************************************************************************
//display: Displays the strings in the list.
//******************************************************************************
void StringList::display()
{
StringNode *p;
p = head;
while (p != NULL)
{
cout << p->data << " ";
p = p->next;
}
cout << endl;
}
//******************************************************************************
//minimum: return the string in alphabetical order
//******************************************************************************
string StringList::minimum()
{
StringNode *p = head;
string minimum = p->data;
while (p->next != NULL)
{
p = p->next;
if(minimum > p->data)
{
minimum = p->data;
}
}
return minimum;
}
//******************************************************************************
//sort: will call the minimum function and remove function
//******************************************************************************
void StringList::sort()
{
StringNode* newhead; // create a new head pointer
string mini;
bool removed;
//adding the first node to the new list.
StringNode *newnode = new StringNode;
mini = minimum(); // get the minimum from the existing linked list
newnode->data = mini;
newnode->next = NULL;
newhead=newnode; //add the minimum node to the new list(with the newhead)
StringNode *p = newhead;
while (head != NULL) // loop should run until there's no node left in the original list
{
StringNode *newnode = new StringNode;
mini = minimum(); // get the minimum from the existing linked list
newnode->data = mini;
newnode->next = NULL;
p->next=newnode; //add the minimum node to the new list(with the newhead pointer)
removed = remove(mini);
p=p->next;
}
head=newhead; //finally change the head pointer, so that the head now points to sorted list.
}
// StringList.h
#ifndef STRINGLIST_H_INCLUDED
#define STRINGLIST_H_INCLUDED
#include <string>
using namespace std;
class StringList
{
private:
struct StringNode // the Nodes of the linked list
{
string data; // data is a string
StringNode *next; // points to next node in list
};
StringNode *head; // the head pointer
public:
StringList();
~StringList();
int count();
void add(string);
bool remove(string);
void display();
string minimum();
void sort();
};
#endif // STRINGLIST_H_INCLUDED
//Driver.cpp
#include<iostream>
#include<iomanip>
using namespace std;
#include "StringList.h"
int main()
{
//testing StringList
StringList slist;
string movie1 = "Star Wars";
string movie2 = "Fargo";
string movie3 = "Back to the Future";
string movie4 = "Titanic";
// Testing add/display/count
cout << "Testing add/display/count: " << endl;
cout << "count is: " << slist.count() << endl;
slist.add(movie1);
slist.display();
cout << "count is: " << slist.count() << endl;
slist.add(movie2);
slist.display();
cout << "count is: " << slist.count() << endl;
slist.add(movie3);
slist.add(movie4);
slist.display();
cout << "count is: " << slist.count() << endl;
// Testing remove
cout << endl;
cout << "Testing remove: " << endl;
bool delResult;
delResult = slist.remove(movie4);
cout << "remove result movie4 = " << boolalpha << delResult << endl;
delResult = slist.remove(movie3);
cout << "remove result movie3 = " << boolalpha << delResult << endl;
delResult = slist.remove("Not There");
cout << "remove result Not There = " << boolalpha << delResult << endl;
cout << "display after remove: " << endl;
slist.display();
cout << "count is: " << slist.count() << endl;
//Testing minimum
cout << endl;
cout << "Testing minimum: " << endl;
cout << "Test minimum 1: " << endl;
slist.display();
cout << "minimum: " << boolalpha << slist.minimum() << endl;
cout << "Test minimum 2: " << endl;
slist.add(movie4);
slist.display();
cout << "minimum: " << boolalpha << slist.minimum() << endl;
cout << "Test minimum 3: " << endl;
slist.add(movie3);
slist.display();
cout << "minimum: " << boolalpha << slist.minimum() << endl;
//Testing sort and display
cout << endl;
cout << "Testing sort/display: " << endl;
slist.sort();
slist.display();
cout << endl;
cout << "Testing sort/display after add: " << endl;
slist.add("Jurassic Park");
slist.display();
cout << "now sorted: " << endl;
slist.sort();
slist.display();
}
您的删除功能有小毛病。 您没有考虑删除第一个节点的可能性。
bool StringList::remove(string movie)
{
StringNode *p = head;
StringNode *n = NULL;
if(p->data==movie) //added this condition
{
head=head->next;
delete p;
return true;
}
while (p != NULL && p->data != movie )
{
n = p;
p = p->next;
if (p == NULL )
{
return false;
}
else if (p->data == movie)
{
n->next = p->next;
delete p;
return true;
}
}
}
最终排序功能。 目的是通过使用minimum和remove函数对现有列表进行排序,并获得新的排序列表。 您需要从现有列表中获取最小值,然后继续将其添加到新列表的末尾。 最后更改头部指针,使其指向新列表。
while循环应运行到现有列表变为空为止。
void StringList::sort()
{
string mini;
bool removed;
//adding the first node to the new list.
StringNode *newnode1 = new StringNode;
mini = minimum(); // get the minimum from the existing linked list
newnode1->data = mini;
newnode1->next = NULL;
removed =remove(mini);
StringNode *p = newnode1;
while (head != NULL) // the loop should run until the original list is empty
{
StringNode *newnode = new StringNode;
mini = minimum(); // get the minimum from the existing linked list
newnode->data = mini;
newnode->next = NULL;
p->next=newnode; //add the minimum node to the new list
removed = remove(mini);
p=p->next;
}
head=newnode1; //finally change the head pointer, so that the head now points to sorted list.
}
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