Hello! In C I want to split a linkedlist into 4 other linked lists.

Question

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I first do a cycle to see how many elements the original list has, then divide by 4 (and multiply by 4) to place it in 4 other lists.
There are the codes:

C

int osszkerdes(Adatok *lista) {
    int szamlalo = 0;
    Adatok *current = lista;
    while (current != NULL) {
        szamlalo++;
        current = current->kovetkezo;
    }
    return szamlalo;
}

void szetszed(Adatok **eredeti_lista, Adatok **lista1, Adatok **lista2, Adatok **lista3, Adatok **lista4) {
    int osszesElem = osszkerdes(eredeti_lista);
    int reszMeret = osszesElem / 4;

    Adatok *aktualis = eredeti_lista;
    for (int i = 0; i < osszesElem; ++i) {
        Adatok *kovetkezo = aktualis->kovetkezo;

        if (i < reszMeret) {
            hozzafuz(*lista1, aktualis);
        } else if (i < 2 * reszMeret) {
            hozzafuz(*lista2, aktualis);
        } else if (i < 3 * reszMeret) {
            hozzafuz(*lista3, aktualis);
        } else {
            hozzafuz(*lista4, aktualis);
        }

        aktualis = kovetkezo;
    }
}</pre lang+C">
The main: 
<pre>Adatok* elso = beolvas_fajlbol("C:\\Users\\Zephyrus\\Desktop\\szoveg.csv");
        Adatok *lista1 = NULL;
        Adatok *lista2 = NULL;
        Adatok *lista3 = NULL;
        Adatok *lista4 = NULL;
      szetszed(elso, &lista1, &lista2, &lista3, &lista4);
      felszabadit(elso);
      felszabadit(lista1);
    felszabadit(lista2);
    felszabadit(lista3);
    felszabadit(lista4);

What I have tried:

Tried to debugg but didnt work for me

Posted 24-Nov-23 5:02am

420bela

Updated 24-Nov-23 8:05am

Andre Oosthuizen

v2

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Comments

CHill60 24-Nov-23 11:04am

You've forgotten to tell us what the problem is

420bela 24-Nov-23 11:09am

The program doesn't do anything, I have a program (debugmalloc) that prints out if there is a memory leak and such, it doesn't even print that.I mean, there are some basic things that work, but after I modified my pogram with the codes I pasted in, it doesn't work.

jeron1 24-Nov-23 11:33am

"The program doesn't do anything" is not a lot to go on. Can you set breakpoints and step through the code? or add lots of printf()'s? Is your list being populated properly? Problem in the felsazabadit() function?

Rick York 24-Nov-23 11:33am

The code you posted is not complete. It lacks the functions hozzafuz and osszkerdes and the type Adatok is not included either. It also lacks beolvas_fajlbol.

420bela 24-Nov-23 11:49am

I have only copied the codes that are likely to contain the error. Since I have a "big" list I would like to change to 4 smaller ones. The mentioned functions work correctly for the big list so I guess the error is in the copied code

Rick York 24-Nov-23 14:22pm

If all of your code was present we could build ourselves and see what's going on. As it is, we can only guess.

2 solutions

Solution 1

Do you need to retain order in the smaller lists? If not, consider using a simple round-robin assignment to produce your smaller lists. Here's a very simple example of how you might do that

C

#include <stdio.h>
#include <stdlib.h>

/* create a simple list */
typedef struct list {
    int datum;
    struct list *next;
} List;


/* simple "push" function, returns a new list with new datum at the front */
List *push(List *list, int datum)
{
    List *item = malloc(sizeof list);
    item->datum = datum;
    item->next = list;
    return item;
}

void show_list(List *list)
{
    while(list) {
        printf("%d ", list->datum);
        list = list->next;
    }
    putchar('\n');
}

int main()
{
    List *list = NULL;

    /* create a list of 12 integers */
    for(int i = 12; i > 0; --i)
        list = push(list, i);

    printf("List : ");
    show_list(list);
    putchar('\n');

    List *lists[4] = { NULL, NULL, NULL, NULL };
    size_t index = 0;

    /* put a member of initial list into one of the lists */
    for(List *tmp = list; tmp != NULL; tmp = tmp->next) {
        lists[index] = push(lists[index], tmp->datum);
        index = (index + 1) % 4;  /* mod 4 cycles index from 0 .. 3 */
      }

    /* show the 4 lists */
    for(int n = 0; n < 4; ++n) {
        printf("list %d : ", n);
        show_list(lists[n]);
    }

    /* free memory here  ... ommited for brevity */
                  
    return 0;
}

running this we get

Terminal

[k5054@localhost] $ ./list
List : 1 2 3 4 5 6 7 8 9 10 11 12 

list 0 : 9 5 1 
list 1 : 10 6 2 
list 2 : 11 7 3 
list 3 : 12 8 4 
[k5054@localhost] $

Note that the smaller lists are in reverse order and contain every 4th element from the larger list. So this may not be what you want if you need to maintain the order of the larger list.

Posted 24-Nov-23 6:10am

k5054

Comments

420bela 24-Nov-23 12:13pm

Sorry ,but the first list should contain the FIRST x items of the original list and so on.

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merano99 · Accepted Answer · 2023-11-24T10:21:00

Solution 2

To write the program as described, some parameters would have to be defined differently.

C

void hozzafuz(Adatok** head, Adatok* aktualis);

//void szetszed(Adatok** eredeti_lista, Adatok** lista1, Adatok** lista2, Adatok** lista3, Adatok** lista4)
void szetszed(Adatok* eredeti_lista, Adatok** lista1, Adatok** lista2, Adatok** lista3, Adatok** lista4)
{
    int osszesElem = osszkerdes(eredeti_lista);
    int reszMeret = osszesElem / 4;

    Adatok* aktualis = eredeti_lista;
    for (int i = 0; i < osszesElem; ++i) {
        if (i < reszMeret) {
            // hozzafuz(*lista1, aktualis);
            hozzafuz(lista1, aktualis);
        }
        else if (i < 2 * reszMeret) {
        ...
        }
        aktualis = aktualis->next;
    }
}

Example Output:
21160, 1952, 30909, 8715, 27167, 22552, 17665, 32119, 11123, 23700, 5219, 22031, 13750, 18673, 22556, 29110, 10890, 7768, 6784,
21160, 1952, 30909, 8715,
22552, 17665, 32119, 11123,
5219, 22031, 13750, 18673,
29110, 10890, 7768, 6784,

Posted 24-Nov-23 10:21am

merano99

Updated 24-Nov-23 14:51pm

v3

Comments

420bela 25-Nov-23 5:23am

seems great but didnt work for me :(

merano99 25-Nov-23 5:37am

After I added the missing parts, the solution seems to work. I had tested it, of course. What exactly is not working yet?

420bela 25-Nov-23 5:46am

It does nothing but blink the cursor. I corrected everything you wrote.
#ifndef NEHEZSEG_H_INCLUDED
#define NEHEZSEG_H_INCLUDED
#include "bevas.h"
int osszkerdes(Adatok *lista);
void szetszed(Adatok* eredeti_lista, Adatok** lista1, Adatok** lista2, Adatok** lista3, Adatok** lista4);

#endif // NEHEZSEG_H_INCLUDED

#include "nehezseg.h"
#include "bevas.h"
int osszkerdes(Adatok *lista) {
int szamlalo = 0;
Adatok *current = lista;
while (current != NULL) {
szamlalo++;
current = current->kovetkezo;
}
return szamlalo;
}
void szetszed(Adatok* eredeti_lista, Adatok** lista1, Adatok** lista2, Adatok** lista3, Adatok** lista4) {
int osszesElem = osszkerdes(eredeti_lista);
int reszMeret = osszesElem / 4;

Adatok *aktualis = eredeti_lista;
for (int i = 0; i < osszesElem; ++i) {
if (i < reszMeret) {
hozzafuz(lista1, aktualis);
} else if (i < 2 * reszMeret) {
hozzafuz(lista2, aktualis);
} else if (i < 3 * reszMeret) {
hozzafuz(lista3, aktualis);
} else {
hozzafuz(lista4, aktualis);
}

aktualis = aktualis->kovetkezo;
}
}
Adatok* elso = beolvas_fajlbol("C:\\Users\\Zephyrus\\Desktop\\szoveg.csv");
Adatok *lista1 = NULL;
Adatok *lista2 = NULL;
Adatok *lista3 = NULL;
Adatok *lista4 = NULL;
szetszed(elso, &lista1, &lista2, &lista3, &lista4);
felszabadit(elso);
felszabadit(lista1);
felszabadit(lista2);
felszabadit(lista3);
felszabadit(lista4);

420bela 25-Nov-23 5:47am

My hozzafuz is like that: void hozzafuz(Adatok* eleje, Adatok* uj) {
Adatok *jelenlegi = eleje;
while (jelenlegi->kovetkezo != NULL) {
jelenlegi = jelenlegi->kovetkezo;
}
jelenlegi->kovetkezo = uj;
}
Is can be the problem?

merano99 25-Nov-23 6:32am

This function is far from what it should be. Please open a new question for this. Also use the prototype I suggested, otherwise it won't work.