List With Iterator(STL)

实现标准模板库中的功能

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

template<class T>
class list {
public:
struct listelem;  // forward declarations
//  也可将struct和iterator的定义直接放在前面
class iterator;
// 构造函数
list() {
h.ptr = t.ptr = NULL;
}
//  注意构造函数中,首先都应该将head和tail置为NULL
//  n个值为c的链表
list(size_t n_elements, const T& c) {
h.ptr = t.ptr = NULL;
for (size_t i = 0; i < n_elements; ++i) {
//  此处用push_front和push_back都可以
push_back(c);
}
}
list(const list& x) {
h.ptr = t.ptr = NULL;  //  重要
list::iterator iter = x.begin();
while (iter != NULL) {
//  下面两句等价于push_back(*iter++);
push_back(*iter);
iter++;
}
}
list(iterator b, iterator e) {
h.ptr = t.ptr = NULL;
while (b != e) {
//  等价于push_back(*b++);
push_back(*b);
b++;
}
}
~list() {
this->clear();
}
iterator begin() const {
return h;
}
iterator end() const {
//  返回的是最后一个迭代器的下一个
iterator temp;
return (temp.ptr == NULL ? iterator(0) : ++temp);
}
size_t size() {
size_t count = 0;
iterator temp = h;
while (temp != end()) {
temp++;
count++;
}
return count;
}
void push_front(const T& c) {
listelem* temp = new listelem(c, h, NULL);
if (empty()) {  //  链表为空时或是if(h == NULL)
// 或是if(h.ptr == NULL)
h.ptr = t.ptr = temp;
} else {   //  链表不为空时
h->prev = temp;
h.ptr = temp;
}
}
void push_back(const T& c) {
listelem* temp = new listelem(c, NULL, t);
if (empty()) {
h.ptr = t.ptr = temp;
} else {
t->next = temp;
t.ptr = temp;
}
}
void pop_front() {
if (empty()) return;  //   链表为空的情况
listelem* temp = h.ptr;
if (h.ptr == t.ptr) {
//  只有一个节点的情况
h.ptr = NULL;
t.ptr = NULL;
delete temp;
} else {
h.ptr = h->next;
h->prev = NULL;
delete temp;
}
}
void pop_back() {
if (empty()) return;
listelem* temp = t.ptr;
if (h.ptr == t.ptr) {
h.ptr = t.ptr = NULL;
delete temp;
} else {
t.ptr = t->prev;
t->next = NULL;
delete temp;
}
}
iterator insert(iterator position, const T& val) {
listelem* p = position.ptr;
if (p == end()) {  //  或者是p == NULL
push_back(val);
return t;
} else if (p == begin()) {  //  或者是 p->prev == NULL
push_front(val);
return begin();
} else {
listelem* temp = new listelem(val, p, p->prev);
temp->next->prev = temp;
temp->prev->next = temp;
return iterator(temp);
}
}
iterator erase (iterator position) {
listelem* temp = position.ptr;
if (temp == NULL||empty()) return iterator(0);
if (temp == h) {
pop_front();
return h;
}
temp->prev->next = temp->next;
temp->next->prev = temp->prev;
listelem* re = temp->next;
delete temp;
return iterator(re);
}
bool empty() const {
return h.ptr == 0;
}
T& front() {
return *h;
}
T& back() {
return *t;
}
void clear() {
while (h.ptr != 0) {
pop_front();
}
h.ptr = t.ptr = NULL;
}
friend ostream& operator << (ostream& out, const list& x) {
list<T>::iterator p = x.begin();
out << "[";
while (p != 0) {
out << *p << " ";
++p;
}
out << "]";
return out;
}

struct listelem {      // list cell
T data;
listelem *next, *prev;
listelem(const T& s, listelem* n, listelem* p) {
data = s;
next = n;
prev = p;
}
};

class iterator {
public:
friend class list;
explicit iterator(listelem* p = 0) {
ptr = p;
}

iterator(const iterator& other) {
ptr = NULL;
ptr = other.ptr;
}
iterator& operator ++ () {
//  ++p;
ptr = ptr->next;
return *this;
}
iterator& operator -- () {
ptr = ptr->prev;
return *this;
}
iterator operator ++ (int) {
//  p++;
iterator temp = *this;
ptr = ptr->next;
return temp;
}
iterator operator -- (int) {
iterator temp = *this;
ptr = ptr->prev;
return temp;
}
listelem* operator -> () {
return ptr;
}
T& operator * () {
return ptr->data;
}
operator listelem * () {
return ptr;
}  // conversion;
private:
listelem* ptr;  // current listelem or 0;
};

private:
iterator h, t;  // head and tail
};

下面是main函数部分

int main() {
list<int> li;
cout << "test size" << endl;
cout << li.size() << endl;
cout << (li.empty() ? "empty" : "not empty") << endl;
int n;  // n >= 3
cout << "test push and pop" << endl;
li.push_back(1);
cout << li << endl;
li.pop_back();
cout << li << endl;
li.push_front(1);
cout << li << endl;
li.pop_front();
cout << li << endl;
li.push_back(1);
cout << li << endl;
li.pop_front();
cout << li << endl;
li.push_front(1);
cout << li << endl;
li.pop_back();

cin >> n;
for (int i = 0; i < n; i++) {
int tmp;
cin >> tmp;
li.push_back(tmp);
li.push_front(tmp);
}
cout << li.size() << endl;
cout << li << endl;
li.pop_back();
li.pop_front();
li.pop_front();
cout << li << endl;
cout << "front : " << li.front() << endl;
cout << "back : " << li.back() << endl;
cout << (li.empty() ? "empty" : "not empty") << endl;

cout << "test begin and end" << endl;
list<int>::iterator it = li.begin();
while (it != li.end()) {
cout << it->data << " ";
it++;
}
cout << endl;

cout << "test insert and erase and ++ --" << endl;
it = li.begin();
cout << *(li.insert(it, 100)) << endl;
it = li.end();
cout << *(li.insert(it, 200)) << endl;
cout << li << endl;
it = li.begin();
cout << *(li.erase(++it)) << endl;
it = li.begin();
it++;
cout << *(li.erase(it)) << endl;
cout << li << endl;
it = li.begin();
it++;
it--;
li.insert(it, 101);
it = li.begin();
++it;
--it;
li.insert(it, 99);
cout << li << endl;
it = li.begin();
*it = 90;

cout << "test constructor" << endl;
list<int> li2(5, 9);
list<int> li3(li);
it = li.begin();
list<int>::iterator it2 = it;
++(++(++it2));
list<int> li4(li.begin(), li.end());
list<int> li5(it, it2);
cout << li2 << endl;
cout << li3 << endl;
cout << li4 << endl;
cout << li5 << endl;

return 0;
}

input :

4

1 2 3 4

output:

test size

0

empty

test push and pop

[1 ]

[]

[1 ]

[]

[1 ]

[]

[1 ]

4

1

2

3

4

8

[4 3 2 1 1 2 3 4 ]

[2 1 1 2 3 ]

front : 2

back : 3

not empty

test begin and end

2 1 1 2 3

test insert and erase and ++ –

100

200

[100 2 1 1 2 3 200 ]

1

1

[100 1 2 3 200 ]

[99 101 100 1 2 3 200 ]

test constructor

[9 9 9 9 9 ]

[90 101 100 1 2 3 200 ]

[90 101 100 1 2 3 200 ]

[90 101 100 ]