如何从C中的链表建立霍夫曼树？

Question

i have a sorted linked list but and I've tried the following code to create a tree and print it. But I'm unable to get the output..

NODE insertorder(NODE first,int pixel,int freq, NODE llink,NODE rlink)
{
    NODE temp=(NODE)malloc(sizeof(struct node));
    NODE cur,prev=NULL;
    temp->pix=pixel;
    temp->freq=freq;
    temp->llink=llink;
    temp->rlink=rlink;
    temp->link=NULL;
    if(first==NULL)
        return temp;
    cur=first;
    while(cur!=NULL&&freq>cur->freq)
    {
        prev=cur;
        cur=cur->link;
    }
    temp->link=cur;
    if(prev!=NULL)
        prev->link=temp;
    return first;
}
      void roots(NODE first)

        {
        NODE t1=first,t2=first->link;//taking first two elements in the list everytime

        if(t2!=NULL)
            createtree(t1,t2);
    }
     void createtree(NODE first,NODE nxt)
    {
       NODE temp=(NODE)malloc(sizeof(struct node));
       temp->pix=0;
       temp->freq=first->freq+nxt->freq;
       temp->llink=first;
       temp->rlink=nxt;
       temp->link=NULL;
       first=deletefirst(first);
       first=deletefirst(first);
       //inserting back the new sum of both elements into the same list
       first=insertorder(first, temp->pix, temp->freq, temp->llink, temp->rlink); 
       roots(first);//calling root back
    }
    printleaf(NODE first,int a[500],int current)
    {
        if(first->llink!=NULL)
        {
            a[current]=0;
            printleaf(first->llink,a,current+1);
        }
        if(first->rlink!=NULL)
        {
            a[current]=1;
            printleaf(first->rlink,a,current+1);
        }
        if(first->llink==NULL&&first->rlink==NULL)
            for(int i=0;a[i]!='\0';i++)
             printf("%d",a[i]);
    }    

My idea is to store back the tree root into the same list that was there before but when i execute it i did not get the output.

Answer 1

In link list if there are rlink and link then it is double link list and from code it is not clear why link is required. When inserting, rlink and link should be used where at insert point both previous node and next nodes has to arrange their rlink and link.