数据结构：带头结点单链表实现--一种非常好的写法（考研）

#include <bits/stdc++.h>
using namespace std;


struct node {
	int val;
	node *next;
	
	node(int x, node *next) {
		this->val = x;
		this->next = next; 
	}
}; 

node *head;
int size = 0;

int getSize() {return size;}


bool isEmpty() {return size == 0;}

//[0,size] 
void insert(int index, int x) {
	if (index<0 || index>size) {
		cout << "the index is invalid!" << endl;
		return;
	}
	
	node *p = head;
	for (int i=0; i<index; ++i) p = p->next;
	node *q = new node(x, p->next);
	p->next = q;
	size ++;
	
}
void insertTail(int x) {
	insert(size, x);
}
void insertHead(int x) {
	insert(0, x);
}
//[0,size-1]
void del(int index) {
	if (index<0 || index>=size) {
		cout << "the index is invalid" << endl;
		return; 
	}
	
	if (isEmpty()) {
		cout << "the LinkedList is null!" << endl;
		return;
	}
	
	node *p = head;
	for (int i=0; i<index; ++i) p = p->next;
	node *del = p->next;
	p->next = del->next;
	delete del;
	size --;
}
void delFirst() {del(0);}
void delLast() {del(size-1);}

//[0,size-1]
int get(int index) {
	if (index<0 || index>=size) {
		cout << "the index is invalid!" << endl;
		return -1; 
	}
	
	if (isEmpty()) {
		cout << "the LinkedList is null!" << endl;
		return -1;
	}
	node *p = head->next;
	for (int i=0; i<index; ++i) p = p->next;
	return p->val;
}
int getLast() {return get(size-1);}
int getFirst() {return get(0);}

void show() {
	node *p = head->next;
	while (p) {
		cout << p->val << " ";
		p = p->next;
	}
	cout << endl;
}

int main() {
	head = new node(0, NULL);
	int a[] = {1,2,3,4,5};
	int n = sizeof(a)/sizeof(int);
	for (int i=0; i<n; ++i) insertTail(a[i]);
	show();
	delFirst();
	show();
	delLast();
	show();
	
	
	cout << get(2) << endl;
	cout << getFirst() << endl;
	cout << getLast() << endl;
	return 0;
}