This is my function for add an element at the end of my lista but I can't find a way for fix the loop in the while, can u give me some tips/rules for make this function work?
void insCoda(t_lista *l, TipoElemLista elem){
t_lista ultimo;
t_lista temp;
temp=(node *)malloc(sizeof(node));
temp->contenuto=elem;
temp->next= NULL;
if(*l==NULL)
{
*l=temp;
printf("Dentro if");
}else{
ultimo=*l;
while(ultimo->next!=NULL)
{
ultimo=ultimo->next;
ultimo->next=temp;
}
}
}
This is thoroughly broken:
ultimo=*l;
while(ultimo->next!=NULL)
{
ultimo=ultimo->next;
ultimo->next=temp;
}
On entry, you set ultimo to (presumably) the head of the list. Then you advance past it to the next node (ultimo=ultimo->next), and immediately set the next pointer of that node to your newly allocated node (ultimo->next=temp). Except oops, your very next action is to test if the thing you just set is NULL or not (and it isn't, unless malloc failed). So you process your new node, and set its next to itself. And now you're in an infinite loop. If you don't enter the loop (because your head is the only node, so the loop condition fails immediately), you never insert the new node at all (which is nice, because this is saving you from the infinite loop).
A hint: Don't set next inside the loop. While I haven't tested, simply moving the set outside the loop should work:
ultimo=*l;
while(ultimo->next!=NULL)
{
ultimo=ultimo->next;
}
ultimo->next=temp;
so now you traverse to the final node, then make your new node the final node.
Related
Now, I understand that code below works only for root and its children, but I don't know how to expand it. Every node must have children before passing on "grandchildren". Thank you.
void insert_node(IndexTree **root, Node *node) {
IndexTree *temp = (IndexTree*)malloc(sizeof(IndexTree));
memcpy(&temp->value.cs, node, sizeof(Node));
temp->left = NULL;
temp->right = NULL;
temp->tip=1;
if ((*root) == NULL) {
*root = temp;
(*root)->left = NULL;
(*root)->right = NULL;
}
else {
while (1) {
if ((*root)->right == NULL) {
(*root)->right = temp;
break;
}
else if ((*root)->left == NULL) {
(*root)->left = temp;
break;
}
}
}
Use recursive functions.
Trees are recursive data types (https://en.wikipedia.org/wiki/Recursive_data_type). In them, every node is the root of its own tree. Trying to work with them using nested ifs and whiles is simply going to limit you on the depth of the tree.
Consider the following function: void print_tree(IndexTree* root).
An implementation that goes over all values of the trees does the following:
void print_tree(IndexTree* root)
{
if (root == NULL) return; // do NOT try to display a non-existent tree
print_tree(root->right);
printf("%d\n", root->tip);
print_tree(root->left);
}
The function calls itself, which is a perfectly legal move, in order to ensure that you can parse an (almost) arbitrarily deep tree. Beware, however, of infinite recursion! If your tree has cycles (and is therefore not a tree), or if you forget to include an exit condition, you will get an error called... a Stack Overflow! Your program will effectively try to add infinite function calls on the stack, which your OS will almost certainly dislike.
As for inserting, the solution itself is similar to that of printing the tree:
void insert_value(IndexTree* root, int v)
{
if (v > root->tip) {
if (root->right != NULL) {
insert_value(root->right, v);
} else {
// create node at root->right
}
} else {
// same as above except with root->left
}
}
It may be an interesting programming question to create a Complete Binary Tree using linked representation. Here Linked mean a non-array representation where left and right pointers(or references) are used to refer left and right children respectively. How to write an insert function that always adds a new node in the last level and at the leftmost available position?
To create a linked complete binary tree, we need to keep track of the nodes in a level order fashion such that the next node to be inserted lies in the leftmost position. A queue data structure can be used to keep track of the inserted nodes.
Following are steps to insert a new node in Complete Binary Tree. (Right sckewed)
1. If the tree is empty, initialize the root with new node.
2. Else, get the front node of the queue.
……. if the right child of this front node doesn’t exist, set the right child as the new node. //as per your case
…….else If the left child of this front node doesn’t exist, set the left child as the new node.
3. If the front node has both the left child and right child, Dequeue() it.
4. Enqueue() the new node.
I'm now implementing Barnes-Hut Algorithms for simulating N-body problem. I only want to ask about the building-tree part.
There are two functions I made to build the tree for it.
I recursively build the tree, and print the data of each node while building and everything seems correct, but when the program is back to the main function only the root of the tree and the child of the root stores the value. Other nodes' values are not stored, which is weird since I printed them during the recursion and they should have been stored.
Here's some part of the code with modification, which I thought where the problem might be in:
#include<...>
typedef struct node{
int data;
struct node *child1,*child2;
}Node;
Node root; // a global variable
int main(){
.
set_root_and_build(); // is called not only once cuz it's actually in a loop
traverse(&root);
.
}
Here's the function set_root_and_build():
I've set the child pointers to NULL, but didn't show it at first.
void set_root_and_build(){
root.data = ...;
..// set child1 and child2 =NULL;
build(&root,...); // ... part are values of data for it's child
}
And build:
void build(Node *n,...){
Node *new1, *new2 ;
new1 = (Node*)malloc(sizeof(Node));
new2 = (Node*)malloc(sizeof(Node));
... // (set data of new1 and new2 **,also their children are set NULL**)
if(some condition holds for child1){ // else no link, so n->child1 should be NULL
build(new1,...);
n->child1 = new1;
//for debugging, print data of n->child1 & and->child2
}
if(some condition holds for child2){ // else no link, so n->child2 should be NULL
build(new2,...);
n->child1 = new2;
//for debugging, print data of n->child1 & and->child2
}
}
Nodes in the tree may have 1~2 children, not all have 2 children here.
The program prints out the correct data when it's in build() function recursion, but when it is back to main function and calls traverse(), it fails due to a segmentation fault.
I tried to print everything in traverse() and found that only the root, and root.child1, root.child2 stores the value just as what I've mentioned.
Since I have to called build() several times, and even in parallel, new1 and new2 can't be defined as global variables. (but I don't think they cause the problem here).
Does anyone know where it goes wrong?
The traverse part with debugging info:
void traverse(Node n){
...//print out data of n
if(n.child1!=NULL)
traverse(*(n.child1))
...//same for child2
}
You may not be properly setting the children of n when the condition does not hold. You might want this instead:
void set_root_and_build()
{
root.data = ...;
build(&root,...); // ... part are values of data for it's child
}
void build(Node *n,...)
{
n->child1 = n->child2 = NULL;
Node *new1, *new2;
new1 = (Node*) malloc(sizeof(Node));
new2 = (Node*) malloc(sizeof(Node));
// set data of new1 and new2 somehow (read from stdin?)
if (some condition holds for new1)
{
n->child1 = new1;
build(n->child1,...);
//for debugging, print data of n->child1
}
else
free(new1); // or whatever else you need to do to reclaim new1
if (some condition holds for new2)
{
n->child2 = new2;
build(n->child2,...);
//for debugging, print data of n->child2
}
else
free(new2); // or whatever else you need to do to reclaim new2
}
Of course, you should be checking the return values of malloc() and handling errors too.
Also, your traversal is a bit strange as it recurses by copy rather than reference. Do you have a good reason for doing that? If not, then maybe you want:
void traverse(Node *n)
{
...//print out data of n
if (n->child1 != NULL)
traverse(n->child1)
...//same for child2
}
The problem in your tree traversal is that you certainly process the tree until you find a node pointer which is NULL.
Unfortunately when you create the nodes, these are not initialized neither with malloc() nor with new (it would be initialized with calloc() but this practice in cpp code is as bad as malloc()). So your traversal continues to loop/recurse in the neverland of random pointers.
I propose you to take benefit of cpp and change slightly your structure to:
struct Node { // that's C++: no need for typedef
int data;
struct node *child1,*child2;
Node() : data(0), child1(nullptr), child2(nullptr) {} // Makes sure that every created are first initalized
};
And later get rid of your old mallocs. And structure the code to avoid unnecessary allocations:
if(some condition holds for child1){ // else no link, so n->child1 should be NULL
new1=new Node; // if you init it here, no need to free in an else !!
build(new1,...);
n->child1 = new1;
...
}
if (... child2) { ... }
Be aware however that poitners allocated with new should be released with delete and note with free().
Edit: There is a mismatch in your code snippet:
traverse(&root); // you send here a Node*
void traverse(Node n){ // but your function defines an argument by value !
...
}
Check that you didn't overllok some warnings from the compiler, and that you have no abusive cast in your code.
I want to add a Newnode to the end of a list but it crashes and goes into a endless loop.
I am attaching the function:
hope to your help!!
void AddProduct(products **head,products *newProduct)
{
products* current=*head;
if(current == NULL)
{
(*head) =(products *)malloc(1*sizeof(products));
(*head) = newProduct;
current=*head;
return;
}
while(current->nextProduct!=NULL)
{
current=current->nextProduct;
}
//Attaching the new product to the list
current->nextProduct=newProduct;
newProduct->prevous=current;
//SortList(head);
}
When creating a new element, you're both accepting it as an argument, and allocating it yourself inside the function. You're overwriting the newly allocated pointer with the one passed in, it doesn't make any sense.
Also, you're not setting the nextProduct field of the new element.
Finally, you're using too many casts and parentheses.
I have implemented a lock free queue in C using compare and swap based on http://www.boyet.com/articles/LockfreeQueue.html.
Its working great but I'm trying to integrate this queue into a lock free skip-list that i have implemented. I'm using the skip-list as a priority queue and would like to use the lock free queue inside each node to store multiple values when there is a priority collision. however due to the way nodes are managed in the skip list when i detect a priority collision i need to be able to add the item to the queue only if the queue is not empty.
due to the lock free nature of the queue im not sure how to actually perform this operation.
So basically how would i write an atomic enqueue_if_not_empty operation?
EDIT: As it was noticed, I wrote the function with quite the opposite semantics - enqueuing only into an empty queue. I fixed the name to reflect that, and decided to leave it as is just in case someone will be interested. So, this is not the right answer to the question, but do not downvote please, unless you find another reason :)
Below is an attempt to add EnqueueIfEmpty() to the queue implementation in the referenced paper. I did not verify that it works or even compiles.
The basic idea is that you insert a new node right after the head (and not the tail), provided that head's next is currently null (which is the necessary condition for an empty queue). I left additional checks for head being equal to tail, which possibly can be removed.
public bool EnqueueIfEmpty(T item) {
// Return immediately if the queue is not empty.
// Possibly the first condition is redundant.
if (head!=tail || head.Next!=null)
return false;
SingleLinkNode<T> oldHead = null;
// create and initialize the new node
SingleLinkNode<T> node = new SingleLinkNode<T>();
node.Item = item;
// loop until we have managed to update the tail's Next link
// to point to our new node
bool Succeeded = false;
while (head==tail && !Succeeded) {
// save the current value of the head
oldHead = head;
// providing that the tail still equals to head...
if (tail == oldHead) {
// ...and its Next field is null...
if (oldhead.Next == null) {
// ...try inserting new node right after the head.
// Do not insert at the tail, because that might succeed
// with a non-empty queue as well.
Succeeded = SyncMethods.CAS<SingleLinkNode<T>>(ref head.Next, null, node);
}
// if the head's Next field was non-null, another thread is
// in the middle of enqueuing a new node, so the queue becomes non-empty
else {
return false;
}
}
}
if (Succeeded) {
// try and update the tail field to point to our node; don't
// worry if we can't, another thread will update it for us on
// the next call to Enqueue()
SyncMethods.CAS<SingleLinkNode<T>>(ref tail, oldHead, node);
}
return Succeeded;
}
Well, Enqueue-If-Not-Empty appears to be relatively straightforward, but with a limitation: other threads may concurrently remove all previous items from the queue, so that after insertion at the tail is done, the new item might happen to be the first in the queue. Since atomic compare-and-swap operations are done with different fields (enqueuing changes tail.Next while dequeuing advances head), stronger guarantees would require additional complexity not only in this function but at least in Dequeue() as well.
The following changes to the normal Enqueue() method are sufficient:
1) at the function start, check for head.Next being null, and if so, return immediately as the queue is empty.
2) add head.Next!=null into the loop condition in case enqueuing attempts should be stopped if the initially non-empty queue becomes empty before insertion succeeds. This does not prevent the situation I descibed above (because there is a time window between the check for emptiness and the node insertion), but reduces its chance to happen.
3) at the end of the function, only try advancing the tail if the new node was successfully enqueued (like I did in the Enqueue-If-Empty answer).
How to traverse each node of a tree efficiently without recursion in C (no C++)?
Suppose I have the following node structure of that tree:
struct Node
{
struct Node* next; /* sibling node linked list */
struct Node* parent; /* parent of current node */
struct Node* child; /* first child node */
}
It's not homework.
I prefer depth first.
I prefer no additional data struct needed (such as stack).
I prefer the most efficient way in term of speed (not space).
You can change or add the member of Node struct to store additional information.
If you don't want to have to store anything, and are OK with a depth-first search:
process = TRUE;
while(pNode != null) {
if(process) {
//stuff
}
if(pNode->child != null && process) {
pNode = pNode->child;
process = true;
} else if(pNode->next != null) {
pNode = pNode->next;
process = true;
} else {
pNode = pNode->parent;
process = false;
}
}
Will traverse the tree; process is to keep it from re-hitting parent nodes when it travels back up.
Generally you'll make use of a your own stack data structure which stores a list of nodes (or queue if you want a level order traversal).
You start by pushing any given starting node onto the stack. Then you enter your main loop which continues until the stack is empty. After you pop each node from the stack you push on its next and child nodes if not empty.
This looks like an exercise I did in Engineering school 25 years ago.
I think this is called the tree-envelope algorithm, since it plots the envelope of the tree.
I can't believe it is that simple. I must have made an oblivious mistake somewhere.
Any mistake regardless, I believe the enveloping strategy is correct.
If code is erroneous, just treat it as pseudo-code.
while current node exists{
go down all the way until a leaf is reached;
set current node = leaf node;
visit the node (do whatever needs to be done with the node);
get the next sibling to the current node;
if no node next to the current{
ascend the parentage trail until a higher parent has a next sibling;
}
set current node = found sibling node;
}
The code:
void traverse(Node* node){
while(node!=null){
while (node->child!=null){
node = node->child;
}
visit(node);
node = getNextParent(Node* node);
}
}
/* ascend until reaches a non-null uncle or
* grand-uncle or ... grand-grand...uncle
*/
Node* getNextParent(Node* node){
/* See if a next node exists
* Otherwise, find a parentage node
* that has a next node
*/
while(node->next==null){
node = node->parent;
/* parent node is null means
* tree traversal is completed
*/
if (node==null)
break;
}
node = node->next;
return node;
}
You can use the Pointer Reversal method. The downside is that you need to save some information inside the node, so it can't be used on a const data structure.
You'd have to store it in an iterable list. a basic list with indexes will work. Then you just go from 0 to end looking at the data.
If you want to avoid recursion you need to hold onto a reference of each object within the tree.