Question

I wrote a recursive doubly linked C++ functions to delete all the nodes in a doubly linked list having a certain value. Is it possible to optimize this? Thank you.

struct marynode {
    int value;
    marynode* next;
    marynode* prev;
};

void DoubleLinkedListDeleteMultiple(marynode*& llist, int value){
    marynode* tmp = llist;

    if (llist == NULL)
        return;

    if (llist->value == value){
            DoubleLinkedListDeleteMultiple(llist->next, value); 
            if (llist->next == NULL){
                marynode* prev = llist->prev;
                delete llist;
                llist = NULL;
                llist = prev;
                if (llist)
                    llist->next = 0;
            }   
            else if (llist->prev == NULL){
                marynode* next = llist->next;
                delete llist;
                llist = NULL;
                llist = next;
                if (llist)
                    llist->prev = 0;
            }   
            else{
                marynode *x = llist;
                marynode  *mynext = x->next;
                while (x){
                    if (x->value == value){
                        marynode* clara = x->next;
                        marynode* zprev = x->prev;
                        delete x;
                        x = NULL;
                        x = clara;
                        llist = clara;
                        if (llist)
                            llist->prev = zprev;
                    }
                    else {
                        x = mynext;
                    }   
                    if (mynext){
                        mynext = mynext->next;
                    }
                }

            }
    }
    else{
            DoubleLinkedListDeleteMultiple(llist->next, value); 
    }
}

Answer 1

Is something wrong with std::list?

Also, structs + global functions? You probably want to use object oriented constructs like member methods instead.

To optimize this particular code a little, I’d change your recursive call to a while loop.

while(llist != NULL) {
     if(llist->value == value) {
          if(llist->prev) {
              llist->prev->next = llist->next;
          }
          if(llist->next) {
              llist->next->prev = llist->prev;
          }
          node* next = llist->next;
          delete llist;
          llist = next;
     } else {
         llist = llist->next;
     }
}