Arraylist mapping to linkedlist nodes
I was wondering if linked list in O(1) time was possible and found the link above. I do not know java but do know a bit of C, not C++. Can someone explain an approach to this concept? How would you code the array to point to the linked list? Based on my knowledge, I think I understand how to store the nodes in a **array but not sure how it can be connected to the *list that also has those same nodes.
Here is a simple example for this.
#include<stdio.h>
#include<stdlib.h>
struct node {
int id;
struct node *next;
struct node *prev;
};
struct node *nodearray[100];
static struct node *head = NULL, *tail = NULL;
void insert_node (struct node **node,int id) {
struct node *new = NULL;
new = malloc(sizeof(*new));
new->id = id;
if (head == NULL) {
head = new;
new->prev = NULL;
} else {
tail->next = new;
new->prev = tail;
}
tail = new;
printf("Added [%d] at %p\n", id, new);
new->next = NULL;
*node = new;
}
void delete_node (int id) {
struct node *node_to_del , *prev, *next;
node_to_del = nodearray[id];
if(!node_to_del)
return;
printf("Del %p\n", node_to_del);
if (node_to_del == head) {
head = node_to_del->next;
node_to_del->next->prev = NULL;
} else if (node_to_del == tail) {
tail = node_to_del->prev;
node_to_del->prev->next = NULL;
} else {
prev = node_to_del->prev;
next = node_to_del->next;
prev->next = next;
next->prev = prev;
}
free(node_to_del);
node_to_del = NULL;
nodearray[id] = NULL;
}
struct node* find_node (int id) {
return nodearray[id];
}
void list_node(void) {
struct node *ptr = head;
while(ptr) {
printf("ptr[%d] %p\n", ptr->id, ptr);
ptr = ptr->next;
}
}
int main () {
insert_node(&nodearray[1] ,1);
insert_node(&nodearray[2] ,2);
insert_node(&nodearray[3] ,3);
insert_node(&nodearray[4] ,4);
insert_node(&nodearray[5] ,5);
printf("1 at %p \n", nodearray[1]);
printf("2 at %p \n", nodearray[2]);
printf("3 at %p \n", nodearray[3]);
printf("4 at %p \n", nodearray[4]);
printf("5 at %p \n", nodearray[5]);
delete_node(1);
delete_node(2);
delete_node(4);
list_node();
printf("1 at %p \n", nodearray[1]);
printf("2 at %p \n", nodearray[2]);
printf("3 at %p \n", nodearray[3]);
printf("4 at %p \n", nodearray[4]);
printf("5 at %p \n", nodearray[5]);
printf("node at 5 = %p\n", nodearray[5]);
return;
}
