以升序和降序打印链表
问题描述:
我有一项任务,涉及使用菜单修改链接列表并能够按照升序和降序打印。它是以前任务的扩展,我们必须将.dat文件加载到程序中并打印出来。我们的新指令是添加一个名为before的新指针,该指针指向。我不知道如何以降序打印它。我们的教授说了一些关于使用循环的内容,但我很困惑这些都是如何工作的。该代码现在有点马虎,因为我还没有机会清理它。以升序和降序打印链表
#include <iostream>
#include <iomanip>
#include <fstream>
using namespace std;
struct Part
{
int number;
float price;
Part *next;
Part *before;
};
class Inventory
{
protected:
Part *start;
public:
Inventory(void);
void link(Part);
string getFileName(void);
bool checkFileExistence(const string& filename);
void getFile(string filename, ifstream& file);
void PrintInventory (void);
void PrintDescending (void);
void AddPart(void);
void loadFile(void);
void DeleteItem(int);
void DeletePart(void);
};
Inventory inven;
Inventory::Inventory(void)
{
start = NULL;
}
void Inventory::link(Part item)
{
Part *p, *last, *here;
p = new Part;
p->number = item.number;
p->price = item.price;
if (start == NULL)
{
start = p;
start -> next = NULL;
}
else
{
here = start;
if(p->number < here->number)
{
p->next = here;
start = p;
}
else
{
while(p->number > here->number && here->next != NULL)
{
last = here;
here = here->next;
}
if (p->number < here->number)
{
last->next = p;
p->next = here;
}
else
{
here->next = p;
p->next = NULL;
}
}
}
}
void Inventory::PrintInventory()
{
Part *travel;
travel = start;
cout.setf(ios::fixed);
cout.precision(2);
if (travel != NULL)
{
cout << "\nPart #" << setw(13) << "Price" << endl;
}
while (travel != NULL)
{
cout << setw(5) << travel->number;
cout << setw(8) << '$' << setw(6) << travel->price << endl;
travel = travel->next;
}
cout << endl;
}
void Inventory::loadFile()
{
string filename;
filename = getFileName();
Part thing;
cout << endl;
if (!checkFileExistence(filename))
{
cout << "File '" << filename << "' not found." << endl;
return;
}
ifstream infile;
infile.open(filename.c_str());
while(!infile.eof())
{
infile >> thing.number;
infile >> thing.price;
inven.link(thing);
}
cout << "\n Inventory File Loaded. \n\n";
}
void Inventory::PrintDescending()
{
}
int main()
{
char key;
int res;
do{
cout << "Menu:" << endl;
cout << "1) Load Inventory File" << endl;
cout << "2) Add Item to Inventory" << endl;
cout << "3) Remove Item from Inventory" << endl;
cout << "4) Print Inventory in Ascending Order" << endl;
cout << "5) Print Inventory in Descending Order" << endl;
cout << "6) Quit" << endl << endl;
cout << "Option Key: ";
cin >> key;
switch (key){
case '2':
inven.AddPart();
res = 1;
break;
case '3':
inven.DeletePart();
res = 1;
break;
case '1':
inven.loadFile();
res = 1;
break;
case '4':
inven.PrintInventory();
res = 1;
break;
case '5':
inven.PrintDescending();
res = 1;
break;
case '6':
res = 0;
break;
default:
res = 1;
break;
}
}while(res == 1);
}
我省去了添加和删除项目的功能,因为它们不是必需的。我们正在使用的.dat文件包含:
123 19.95
46 7.63
271 29.99
17 .85
65 2.45
32 49.50
128 8.25
答
这是一种经典的数据结构算法。请参阅Double linked list。
但是:
之前试图打印,您需要之前更新与新指针你的代码。你也可以简化这个,看看评论。 所以你链接功能:
if (start == NULL)
{
start = p;
start -> next = NULL;
// Here :
start->before = NULL;
}
else
{
here = start;
// You can remove this if...
if(p->number < here->number)
{
p->next = here;
start = p;
}
else
{
// ... Because your condition in the next while is enough.
while(p->number > here->number && here->next != NULL)
{
last = here;
here = here->next;
}
if (p->number < here->number)
{
// Here : TODO link with the previous one
last->next = p;
p->next = here;
}
else
{
// Here : TODO link with the previous one
here->next = p;
p->next = NULL;
}
}
}
}
,然后再打印,只要把你的PrintInventory功能,但之前使用解析。
希望它有帮助。
看起来你的列表是双向链接的(即有一个'next'和''before'指针)。但是在链接时你并没有使用这个逻辑。你只是连接下一个指针。用双向链表进行反向打印很容易,因为您只需从最后开始并按照“之前”指针。如果您想要反向打印单链表,您可以递归执行,也可以向前遍历列表两次(第一次,将其重新排序;第二次再次反转它,但在打印时按顺序打印每个节点)。 – paddy