数组是一种支持随机访问的数据结构，而链表支持在结构中间某个位置插入和删除数据的时间复杂度$O(1)$的数据结构。
struct Node{
int v;
struct Node *p, *n;
Node(int val): v(val) {}
};
Node* head, * tail;
void initialize(){
head = new Node();
tail = new Node();
head->n = tail;
tail->p = head;
}
void insert(Node* p, int val){
Node* t = new Node(val);
t->n = p->n;
p->n->p = t;
p->n = t;
t->p = p;
}
void remove(Node* p){
p->n->p = p->p;
p->p->n = p->n;
delete p;
}
void free_node(){
Node* t;
while(head){
t = head->n;
delete head;
head = t;
}
}
1. 邻接表
const int N = BUFSIZE;
int idx = 1;
int h[N], e[N], ne[N], w[N];
void add(int a, int b, int c){
e[idx] = b, w[idx] = c, ne[idx] = h[a], h[a] = idx++;
}
void visit(int x){
for(int i = h[x]; i; i = ne[i]){
int j = e[i];
// todo:
}
}