我正在學習資料結構，我創建了一個帶有追加方法的鏈表，如下所示：
#include<iostream>
class List{
public:
using value_type = double;
using reference = value_type&;
using const_reference = value_type const &;
List()
: head_(nullptr)
, tail_(nullptr)
{}
void append(const_reference data){
Node* node = new Node;
node->data = data;
node->next = nullptr;
if(head_ == nullptr){
head_ = node;
return;
}
if(tail_ == nullptr){
tail_ = node;
head_->next = tail_;
return;
}
tail_->next = node;
Node* temporary = tail_;
tail_ = node;
node = temporary;
}
void print(){
Node* temporary = head_;
while(temporary != nullptr){
std::cout << temporary->data << '-';
temporary = temporary->next;
}
}
struct Node{
value_type data;
Node* next;
};
Node* head_;
Node* tail_;
};
int main(){
List list;
list.append(1);
list.append(2);
list.append(3);
list.append(4);
list.print();
return 0;
}
但后來閱讀如何去做，我發現了這樣的事情：
void Append (Node* head, int data) {
Node* current = head;
while (current->next != nullptr) {
current = current->next;
}
Node* new_node = new Node(data);
current->next = new_node;
}
我不是專家購買我不認為遍歷所有節點，只是在最后附加一些東西是有效的，我錯了嗎？
uj5u.com熱心網友回復：
您的代碼有效。盡管實作起來有點非正統，但它甚至是高效的。因為，它使用尾指標直接在末尾追加一個元素。
超好的。
您顯示的另一個代碼片段適用于沒有尾指標的單向鏈表。是的，對于這個用例，這有點低效。而且，這樣的串列也有其用例，它們在這些用例中表現非常好。在 C 標準庫中，這樣的串列稱為forward_list。
更經常std::list使用。這是一個雙向鏈表。您可以輕松地雙向遍歷這樣的串列，這也是它的主要優點。它使用頭指標和尾指標，但不像您實作的那樣。它使用一個哨兵，一個始終存在并包含的特殊節點，可以說是頭指標和尾指標。
因此，您使用的是混合動力，它只允許向前遍歷，您使用尾指標進行優化以直接訪問最后一個元素。但是如果你想在串列的中間做一些事情，那么你必須從頭開始向前遍歷它。
因此，具有下一個和上一個指標的節點可能更可取。但這取決于您的用例。
出于學習目的，我在下面向您展示了一個雙向鏈表。也許你可以從中得出一些想法。
#include <iterator>
#include <initializer_list>
#include <algorithm>
#include <iostream>
#include <type_traits>
#include <vector>
// ------------------------------------------------------------------------------------------------
// This would be in a header file -----------------------------------------------------------------
// Type trait helper to identify iterators --------------------------------------------------------
template<typename T, typename = void>
struct is_iterator { static constexpr bool value = false; };
template<typename T>
struct is_iterator<T, typename std::enable_if<!std::is_same<typename std::iterator_traits<T>::value_type, void>::value>::type> {
static constexpr bool value = true;
};
// The List class ---------------------------------------------------------------------------------
template <typename T>
class List {
// Sub class for a Node -----------
struct Node {
T data{};
Node* next{};
Node* previous{};
Node() {}
Node(Node* const n, Node* const p) : next(n), previous(p) {}
Node(Node* const n, Node* const p, const T& d) : next(n), previous(p), data(d) {}
};
// Private list data and functions --------
Node* head{};
size_t numberOfElements{};
void init() { head = new Node(); head->next = head; head->previous = head; numberOfElements = 0; }
public:
struct iterator; // Forward declaration
// Constructor --------------------
List() { init(); }
explicit List(const size_t count) { init(); insert(begin(), count); }
explicit List(const size_t count, const T& value) { init(); insert(begin(), count, value); };
template <typename Iter>
List(const Iter& first, const Iter& last) { init(); insert(begin(), first, last); }
List(const List& other) { init(), insert(begin(), other.begin(), other.end()); };
List(List&& other) : head(other.head), numberOfElements(other.numberOfElements) { other.init(); }
List(const std::initializer_list<T>& il) { init(); insert(begin(), il.begin(), il.end()); }
template <int N> List(T(&other)[N]) { init(); insert(begin(), std::begin(other), std::end(other)); }
template <int N> List(const T(&other)[N]) { init(); insert(begin(), std::begin(other), std::end(other)); }
// Assignment ---------------------
List& operator =(const List& other) { clear(); insert(begin(), other.begin(), other.end()); return *this; }
List& operator =(List&& other) { clear(); head = other.head; numberOfElements = other.numberOfElements; other.init(); return *this; }
List& operator =(const std::initializer_list<T>& il) { clear(); insert(begin(), il.begin(), il.end()); return *this; }
template <int N> List& operator =(const T(&other)[N]) { clear(); insert(begin(), std::begin(other), std::end(other)); return *this; }
template <int N> List& operator =(T(&other)[N]) { clear(); insert(begin(), std::begin(other), std::end(other)); return *this; }
template <typename Iter> void assign(const Iter& first, const Iter& last) { clear(); insert(begin(), first, last); }
template <int N> void assign(const T(&other)[N]) { clear(); insert(begin(), std::begin(other), std::end(other)); return *this; }
template <int N> void assign(T(&other)[N]) { clear(); insert(begin(), std::begin(other), std::end(other)); return *this; }
void assign(const size_t count, const T& value) { clear(); insert(begin(), count, value); }
void assign(const std::initializer_list<T>& il) { clear(); insert(begin(), il.begin(), il.end()); }
// Destructor ---------------------
~List() { clear(); }
// Element Access -----------------
T& front() { return *begin(); }
T& back() { return *(--end()); }
// Iterators ----------------------
iterator begin() const { return iterator(head->next, head); }
iterator end() const { return iterator(head, head); }
// Capacity -----------------------
size_t size() const { return numberOfElements; }
bool empty() { return size() == 0; }
// Modifiers ----------------------
void clear();
iterator insert(const iterator& insertBeforePosition, const T& value);
iterator insert(const iterator& insertBeforePosition);
template <class Iter, std::enable_if_t<is_iterator<Iter>::value, bool> = true>
iterator insert(const iterator& insertBeforePosition, const Iter& first, const Iter& last);
iterator insert(const iterator& insertBeforePosition, const size_t& count, const T& value);
iterator insert(const iterator& insertBeforePosition, const std::initializer_list<T>& il);
iterator erase(const iterator& posToDelete);
iterator erase(const iterator& first, const iterator& last);
void pop_front() { erase(begin()); };
void push_front(const T& d) { insert(begin(), d); }
void pop_back() { erase(--end()); };
void push_back(const T& d) { insert(end(), d); }
void resize(size_t count, const T& value);
void resize(size_t count);
void swap(List& other) { std::swap(head, other.head); std::swap(numberOfElements, other.numberOfElements); }
// Operations --------------------
void reverse();
// Non standard inefficient functions --------------------------
T& operator[](const size_t index) const { return begin()[index]; }
// ------------------------------------------------------------------------
// Define iterator capability ---------------------------------------------
struct iterator {
// Definitions ----------------
using iterator_category = std::bidirectional_iterator_tag;
using difference_type = std::ptrdiff_t;
using value_type = T;
using pointer = T*;
using reference = T&;
// Data -----------------------
Node* iter{};
Node* head{};
// Constructor ----------------
iterator(Node* const node, Node* const h) : iter(node), head(h) {};
iterator() {};
// Dereferencing --------------
reference operator*() const { return iter->data; }
reference operator->() const { return &**this; }
// Arithmetic operations ------
iterator operator () { iter = iter->next; return *this; }
iterator operator--() { iter = iter->previous; return *this; }
iterator operator (int) { iterator tmp = *this; * this; return tmp; }
iterator operator--(int) { iterator tmp = *this; --* this; return tmp; }
iterator operator (const difference_type& n) const {
iterator temp{ *this }; difference_type k{ n }; if (k > 0) while (k--) temp; else while (k )--temp; return temp;
}
iterator operator =(const difference_type& n) {
difference_type k{ n }; if (k > 0) while (k--) * this; else while (k )--* this; return *this;
};
iterator operator -(const difference_type& n) const {
iterator temp{ *this }; difference_type k{ n }; if (k > 0) while (k--)--temp; else while (k ) temp; return temp;
}
iterator operator -=(const difference_type& n) {
difference_type k{ n }; if (k > 0) while (k--)--* this; else while (k ) * this; return *this;
};
// Comparison ----------------- (typical space ship implementation)
bool operator ==(const iterator& other) const { return iter == other.iter; };
bool operator !=(const iterator& other) const { return iter != other.iter; };
bool operator < (const iterator& other) const { return other.iter - iter < 0; };
bool operator <= (const iterator& other) const { return other.iter - iter <= 0; };
bool operator > (const iterator& other) const { return other.iter - iter > 0; };
bool operator >= (const iterator& other) const { return other.iter - iter >= 0; };
// Special non standard functions -----------------
difference_type operator-(const iterator& other) const;
reference operator[] (const size_t index);
};
};
// ------------------------------------------------------------------------------------------------
// Implementation of list functions. This would normally go into a TCC file -----------------------
// List class functions ---------------
template <typename T>
void List<T>::clear() {
for (Node* nextNode{}, * currentNode(head->next); currentNode != head; currentNode = nextNode) {
nextNode = currentNode->next;
delete currentNode;
}
init();
}
template <typename T>
typename List<T>::iterator List<T>::insert(const List<T>::iterator& insertBeforePosition, const T& value)
{
Node* nodeInsertBeforePosition = insertBeforePosition.iter;
Node* newNode = new Node(nodeInsertBeforePosition, nodeInsertBeforePosition->previous, value);
nodeInsertBeforePosition->previous = newNode;
(newNode->previous)->next = newNode;
numberOfElements;
return iterator(newNode, head);
}
template <typename T>
typename List<T>::iterator List<T>::insert(const List<T>::iterator& insertBeforePosition)
{
Node* nodeInsertBeforePosition = insertBeforePosition.iter;
Node* newNode = new Node(nodeInsertBeforePosition, nodeInsertBeforePosition->previous);
nodeInsertBeforePosition->previous = newNode;
(newNode->previous)->next = newNode;
numberOfElements;
return iterator(newNode, head);
}
template <typename T>
template <class Iter, std::enable_if_t<is_iterator<Iter>::value, bool>>
typename List<T>::iterator List<T>::insert(const List<T>::iterator& insertBeforePosition, const Iter& first, const Iter& last) {
iterator result(insertBeforePosition.iter, head);
if (first != last) {
result = insert(insertBeforePosition, *first);
Iter i(first);
for ( i; i != last; i)
insert(insertBeforePosition, *i);
}
return result;
}
template <typename T>
typename List<T>::iterator List<T>::insert(const List<T>::iterator& insertBeforePosition, const size_t& count, const T& value) {
iterator result(insertBeforePosition.iter, head);
if (count != 0u) {
result = insert(insertBeforePosition, value);
for (size_t i{ 1u }; i < count; i)
insert(insertBeforePosition, value);
}
return result;
}
template <typename T>
typename List<T>::iterator List<T>::insert(const List<T>::iterator& insertBeforePosition, const std::initializer_list<T>& il) {
return insert(insertBeforePosition, il.begin(), il.end());
}
template <typename T>
typename List<T>::iterator List<T>::erase(const List<T>::iterator& posToDelete) {
iterator result = posToDelete;
result;
Node* nodeToDelete = posToDelete.iter;
if (nodeToDelete != head) {
nodeToDelete->previous->next = nodeToDelete->next;
nodeToDelete->next->previous = nodeToDelete->previous;
delete nodeToDelete;
--numberOfElements;
}
return result;
}
template <typename T>
typename List<T>::iterator List<T>::erase(const List<T>::iterator& first, const List<T>::iterator& last) {
iterator result{ end() };
if (first == begin() && last == end())
clear();
else {
while (first != last)
first = erase(first);
result = last;
}
return result;
}
template <typename T>
void List<T>::resize(size_t count) {
if (numberOfElements < count)
for (size_t i{ numberOfElements }; i < count; i)
insert(end());
else
while (count--)
pop_back();
}
template <typename T>
void List<T>::resize(size_t count, const T& value) {
if (numberOfElements < count)
for (size_t i{ numberOfElements }; i < count; i)
insert(end(), value);
else
while (count--)
pop_back();
}
template <typename T>
void List<T>::reverse() {
const Node* oldHead = head;
for (Node* nptr = head; ; nptr = nptr->previous) {
std::swap(nptr->next, nptr->previous);
if (nptr->previous == oldHead) // Previous was the original next
break;
}
}
// ------------------------------------
// Iterator functions -----------------
template <typename T>
typename List<T>::iterator::difference_type List<T>::iterator::operator-(const iterator& other) const {
difference_type result{};
Node* nptr = head;
int indexThis{ -1 }, indexOther{ -1 }, index{};
do {
nptr = nptr->next;
if (nptr == iter)
indexThis = index;
if (nptr == other.iter)
indexOther = index;
index;
} while (nptr != head);
if (indexThis >= 0 and indexOther >= 0)
result = indexThis - indexOther;
return result;
}
template <typename T>
typename List<T>::iterator::reference List<T>::iterator::operator[] (const size_t index) {
Node* nptr = head->next;
for (size_t i{}; i < index and nptr != head; i, nptr = nptr->next)
;
return nptr->data;
}
// ------------------------------------------------------------------------------------------------
// This would be in a cpp file --------------------------------------------------------------------
int main() {
List<int> list3{ 10,20 };
List<int>::iterator l3 = list3.end();
for (int k = 0; k < 10; k) {
std::cout << *l3 << ' ';
--l3;
}
std::cout << '\n';
// Custom list
List<int> list2{ 1, 2, 3, 4, 5 };
for (int i : list2)
std::cout << i << ' '; std::cout << '\n';
// Delta works
std::cout << list2.begin() - list2.end() << '\n';
std::cout << list2.end() - list2.begin() << '\n';
// Hopp Count works
List<int>::iterator i = list2.end();
while (i-- != list2.begin())
std::cout << *i << ' '; std::cout << '\n';
}
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標籤：C 表现数据结构链表