数据结构 - 从一个链表中删除在另一个链表中的元素（C++）

/*
Sort both list from small to big. And then use the following code.
*/

#include <iostream>

using namespace std;

struct Node
{
char data;
Node* next;
};

Node* create()
{
Node* head = NULL;
Node* rear = head;
Node* p; // The pointer points to new created node.
char tmp;

do
{
cout << "Please input integer or char '#':";
cin >> tmp;
if(tmp != '#')
{
p = new Node;
p->data = tmp;
p->next = NULL;

if(head == NULL)
{
head = p;
}
else
{
rear->next = p;
}

rear = p;
}
}
while(tmp != '#');

return head;
}

void print(Node* head)
{
Node* p = head;

if(head != NULL)
{
do
{
cout << p->data << ' ';
p = p->next;
}
while(p != NULL);
}

cout << endl;
}

Node* del(Node* l1, Node* l2)
{
if(!l1 || !l2)
{
return NULL;
}

Node *p = new Node;
p->next = l1;
Node *pL1 = l1, *pL2 = l2, *head = p;

while(pL1 && pL2)
{
if(pL1->data < pL2->data)
{
pL1 = pL1->next;
p = p->next;
}
else if(pL1->data > pL2->data)
{
pL2 = pL2->next;
}
else
{
pL1 = pL1->next;
p->next = pL1;
}
}

l1 = head->next;

return l1;
}

int main()
{
cout << "Please input the first list:" << endl;
Node* l1 = create();

cout << endl << "Please input the second list:" << endl;
Node* l2 = create();

cout << endl << "--------------------------" << endl;
cout << "The first list is: ";
print(l1);
cout << "The second list is: ";
print(l2);

Node* l = del(l1, l2);
cout << endl << "The result list is: ";
print(l);

return 0;
}

// Output:
/*
Please input the first list:
Please input integer or char '#':1
Please input integer or char '#':1
Please input integer or char '#':1
Please input integer or char '#':1
Please input integer or char '#':3
Please input integer or char '#':3
Please input integer or char '#':3
Please input integer or char '#':3
Please input integer or char '#':4
Please input integer or char '#':5
Please input integer or char '#':6
Please input integer or char '#':6
Please input integer or char '#':6
Please input integer or char '#':7
Please input integer or char '#':7
Please input integer or char '#':8
Please input integer or char '#':8
Please input integer or char '#':8
Please input integer or char '#':9
Please input integer or char '#':9
Please input integer or char '#':9
Please input integer or char '#':9
Please input integer or char '#':#

Please input the second list:
Please input integer or char '#':1
Please input integer or char '#':2
Please input integer or char '#':5
Please input integer or char '#':5
Please input integer or char '#':5
Please input integer or char '#':7
Please input integer or char '#':7
Please input integer or char '#':7
Please input integer or char '#':7
Please input integer or char '#':7
Please input integer or char '#':9
Please input integer or char '#':#

--------------------------
The first list is: 1 1 1 1 3 3 3 3 4 5 6 6 6 7 7 8 8 8 9 9 9 9
The second list is: 1 2 5 5 5 7 7 7 7 7 9

The result list is: 3 3 3 3 4 6 6 6 8 8 8
*/