单向链表:

#include <iostream>
#define int long long
using namespace std;
const int N = 1e6 + 5;
struct linkedNode {
	int data;
	linkedNode* next;
};
struct linkedList {
	public:
		int size() { return listSize; } // 输出链表长度，默认是0 
		bool empty() { return listSize == 0; } // 输出链表是否为空
		linkedNode* getIdx(int pos); // 得到一个在第pos个位置的linkedNode类型的指针 
		void insert(int pos, int theElement); // 在链表的第pos个位置插入元素theElement 
		void erase(int pos); // 擦除第pos个位置的元素
	private:
		unsigned int listSize = 0;
		linkedNode* head;
};
linkedNode* linkedList::getIdx(int pos) {
	if (pos < 0 || pos > listSize)
		return nullptr;
	linkedNode* p = head;
	for (int i = 0; i < pos - 1; ++i)
		p = p->next;
	return p; 
}
void linkedList::insert(int pos, int theElement) {
	if (pos < 0 || pos > listSize)
		return;
	linkedNode* insertNode = new linkedNode();
	insertNode->data = theElement;
	if (pos == 0) {
		head = insertNode;
		++listSize;
		return;
	}
	linkedNode* p = getIdx(pos);
	insertNode->next = p->next;
	p->next = insertNode;
	++listSize;
	return;
}
void linkedList::erase(int pos) {
	if (pos < 0 || pos > listSize)
		return;
	linkedNode* deleteNode;
	if (pos == 0) {
		deleteNode = head;
		head = head->next;
	} else {
		linkedNode* p = getIdx(pos);
		deleteNode = p->next;
		p->next = p->next->next;
		delete deleteNode;
		--listSize;
	}
	return; 
}
signed main() {
	ios::sync_with_stdio(false);
	linkedList list;
	// You Code Here...
	return 0;
}

双向链表:

#include <bits/stdc++.h>
#define int long long
using namespace std;
const int N = 1e6 + 5;
struct doubleLinkedNode {
	int data;
	doubleLinkedNode* prev;
	doubleLinkedNode* next;
};
struct doubleLinkedList {
	public:
		int size() { return listSize; } // 输出链表长度，默认是0 
		bool empty() { return listSize == 0; } // 输出链表是否为空 
		doubleLinkedNode* getIdx(int pos); // 得到一个在第pos个位置的doubleLinkedNode类型的指针 
		void insert(int pos, int theElement); // 在链表的第pos个位置插入元素theElement 
		void erase(int pos); // 擦除第pos个位置的元素 
	private:
		unsigned int listSize = 0;
		doubleLinkedNode* head;
};
doubleLinkedNode* doubleLinkedList::getIdx(int pos) {
	if (pos < 0 || pos > listSize)
		return nullptr;
	doubleLinkedNode* p = head;
	for (int i = 0; i < pos - 1; ++i)
		p = p->next;
	return p; 
}
void doubleLinkedList::insert(int pos, int theElement) {
	if (pos < 0 || pos > listSize)
		return;
	doubleLinkedNode* newNode = new doubleLinkedNode();
	newNode->data = theElement;
	if (pos == 0) {
		newNode->next = head;
		if (head != nullptr)
			head->prev = newNode;
		head = newNode;
		++listSize;
		return;
	}
	doubleLinkedNode* curNode = getIdx(pos);
	newNode->next = curNode->next;
	if (curNode->next != nullptr)
		curNode->next->prev = newNode;
	curNode->next = newNode;
	newNode->prev = curNode;
	++listSize;
	return;
}
void doubleLinkedList::erase(int pos) {
	if (pos < 0 || pos > listSize)
		return;
	doubleLinkedNode* deleteNode = nullptr;
	if (pos == 0) {
		deleteNode = head;
		if (head->next != nullptr)
			head->next->prev = nullptr;
		head = head->next;
	} else {
		doubleLinkedNode* curNode = getIdx(pos);
		deleteNode = curNode->next;
		if (deleteNode->next != nullptr)
			deleteNode->next->prev = curNode;
		curNode->next = deleteNode->next;
	}
	--listSize;
	delete deleteNode;
	return;
}
signed main() {
	ios::sync_with_stdio(false);
	doubleLinkedList list;
	// You Code Here...
	return 0;
}