按照要求补充实现Linked List的所有函数并通过测试，不能使用STL中现有的方法。

Here is a C++ class definition for an abstract data type LinkedList of strings. Implement each member function in the class below. Some of the functions we may have already done in lecture, thats fine, try to do those first without looking at your notes. You may add whatever private data members or private member functions you want to this class.

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#include <iostream>
#include <string>
using namespace std;

typedef string ItemType;

struct Node {
  ItemType value;
  Node *next;
};

class LinkedList {

private:
  Node *head;

public:

  // default constructor
  LinkedList() : head(nullptr) { }

  // copy constructor
  LinkedList(const LinkedList& rhs);

  // Destroys all the dynamically allocated memory
  // in the list.
  ~LinkedList();

  // assignment operator
  const LinkedList& operator=(const LinkedList& rhs);
  
  // Inserts val at the front of the list
  void insertToFront(const ItemType &val);

  // Prints the LinkedList
  void printList() const;

  // Sets item to the value at position i in this
  // LinkedList and return true, returns false if 
  // there is no element i
  bool get(int i, ItemType& item) const;

  // Reverses the LinkedList
  void reverseList();

  // Prints the LinkedList in reverse order
  void printReverse() const;

  // Appends the values of other onto the end of this
  // LinkedList.
  void append(const LinkedList &other);

  // Exchange the contents of this LinkedList with the other one.
  void swap(LinkedList &other);

  // Returns the number of items in the Linked List.
  int size() const;
};

When we dont want a function to change a parameter representing a value of the type stored in the LinkedList, we pass that parameter by constant reference. Passing it by value would have been perfectly fine for this problem, but we chose the const reference alternative because that will be more suitable after we make some generalizations in a later problem.

The get function enables a client to iterate over all elements of a LinkedList. In other words, this code fragment

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LinkedList ls;
ls.insertToFront("Jack");
ls.insertToFront("Germaine");
ls.insertToFront("Agatha");
ls.insertToFront("Agnes");

for (int k = 0; k < ls.size(); k++)
{
  string x;
  ls.get(k, x);
  cout << x << endl;
}

must write

AgnesAgathaGermaineJack

The printList and printReverse functions enables a client to print elements of a LinkedList. In other words, this code fragment

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LinkedList ls;
ls.insertToFront("George");
ls.insertToFront("Louise");
ls.insertToFront("Lionel");
ls.insertToFront("Helen");

ls.printList();
ls.printReverse();

must write

Helen Lionel Louise GeorgeGeorge Louise Lionel Helen

You should have one space between after each item printed with an additional newline after the last item.

Here is an example of the append function:

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LinkedList e1;
e1.insertToFront("bell");
e1.insertToFront("biv");
e1.insertToFront("devoe");
LinkedList e2;
e2.insertToFront("Andre");
e2.insertToFront("Big Boi");
e1.append(e2);  // adds contents of e2 to the end of e1
string s;
assert(e1.size() == 5  &&  e1.get(3, s)  &&  s == "Big Boi");
assert(e2.size() == 2  &&  e2.get(1, s)  &&  s == "Andre");

Here is an example of the reverseList function:

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LinkedList e1;
e1.insertToFront("Sam");
e1.insertToFront("Carla");
e1.insertToFront("Cliff");
e1.insertToFront("Norm");

e1.reverseList();  // reverses the contents of e1
string s;
assert(e1.size() == 4  &&  e1.get(0, s)  &&  s == "Sam");

Heres an example of the swap function:

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LinkedList e1;
e1.insertToFront("A");
e1.insertToFront("B");
e1.insertToFront("C");
e1.insertToFront("D");
LinkedList e2;
e2.insertToFront("X");
e2.insertToFront("Y");
e2.insertToFront("Z");
e1.swap(e2);  // exchange contents of e1 and e2
string s;
assert(e1.size() == 3  &&  e1.get(0, s)  &&  s == "Z");
assert(e2.size() == 4  &&  e2.get(2, s)  &&  s == "B");

When comparing items, just use the == or != operators provided for the string type by the library. These do case-sensitive comparisons, and thats fine.

Turn it in

There will be a link on CCLE that will enable you to turn in this homework. Turn in one zip file that contains your solutions to the homework problem. The zip file must contain only the file linkedlist.cpp. The source file will contain all the code from the top of this specification (includes, typedef, struct Node, class LinkedList), a main routine and the LinkedList member functions you will write. If you dont finish everything you should return dummy values for your missing definitions. You can have the main routine do whatever you want, because we will rename it to something harmless, never call it, and append our own main routine to your file. Our main routine will thoroughly test your functions. Youll probably want your main routine to do the same. Your code must be such that if we insert it into a suitable test framework with a main routine and appropriate #include directives, it compiles. (In other words, it must have no missing semicolons, unbalanced parentheses, undeclared variables, etc.)