Merging two linked lists C++

Hello /prog/

I'm having some trouble with a function that is supposed to merge two linked lists. I'm being passed two Linked Lists as parameters and want to know an efficient way of making it so that I can merge these two lists together (duplicates are allowed) without using an insert function. The code that I have is here:
http://pastebin.com/RtUGcYhy

Any help/suggestions/criticism will be appreciated.


merge compare xs [] = xs
merge compare [] ys = ys
merge compare (x:xs) (y:ys) =
  if compare x y
  then x:(merge compare xs (y:ys))
  else y:(merge compare (x:xs) ys)

Pick one.
1. link one's tail to the other's head;
2. insert one's elements into the other;
3. create a third list and insert all elements.

C++ a shit

>>4
You cannot possibly be worse than /prog/.

it could be fast enough. A typical destructive merge.


#include <stdio.h>
#include <string.h>

struct node {
  void* car;
  struct node* cdr;
};

struct node* destructomerge(int (*compare)(void*,void*), struct node* list1, struct node* list2) {
  if (!list1) return list2;
  if (!list2) return list1;
  struct node* head;
  struct node* tail;
  if (compare(list1->car,list2->car) < 0) {
    head = tail = list1;
    list1 = list1->cdr;
  } else {
    head = tail = list2;
    list2 = list2->cdr;
  }
  loop:
  if(!list1) {
    tail->cdr = list2;
    return head;
  } else if(!list2) {
    tail->cdr = list1;
    return head;
  } else if(compare(list1->car,list2->car) < 0) {
    tail->cdr = list1;
    tail = list1;
    list1 = list1->cdr;
    goto loop;
  } else {
    tail->cdr = list2;
    tail = list2;
    list2 = list2->cdr;
    goto loop;
  }
}

void for_each(void (*visitor)(void*), struct node* list) {
  loop:
  if(list) {
    visitor(list->car);
    list = list->cdr;
    goto loop;
  }
}

int main(int argc, char** argv) {
  struct node a1;
  struct node a2;
  struct node a3;
  struct node b1;
  struct node b2;
  struct node b3;
  a1.car = "apples";
  a2.car = "grapes";
  a3.car = "oranges";
  b1.car = "grains";
  b2.car = "meats";
  b3.car = "sugary sweets";
  a1.cdr = &a2;
  a2.cdr = &a3;
  a3.cdr = NULL;
  b1.cdr = &b2;
  b2.cdr = &b3;
  b3.cdr = NULL;
  printf("a1:\n");
  for_each(puts, &a1);
  printf("b1:\n");
  for_each(puts, &b1);
  struct node* merged = destructomerge(strcmp, &a1, &b1);
  printf("merged:\n");
  for_each(puts, merged);
  return 0;
}

I know I did your homework, but I'm hoping you learn something from this example. And it's written in C with bad enough practice to need a rewrite.

After reading your source more carefully, your code looks as efficient as it can be. What did you want to improve about it?

You should avoid writing your own code when you can just use the standard library. It has platform-specific optimizations, and is much easier to maintain.

>>9
WHY U NO STD::STRING ???



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>>11-15
who are you quoting?