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

typedef struct Snode_tag
{
    int data;
    struct Snode_tag *next;
} Snode;

void print_single(Snode *head)
{
    printf("%d", head->data);
    if (head->next) {
        printf(", ");
        print_single(head->next);
    }
}

void print_single_list(Snode *head)
{
    if (head) {
        print_single(head);
        printf("\n");
    } else {
        printf("NULL\n");
    }
}

Snode *make_single(int n)
{
    if (0 == n) return NULL;
    Snode *node = malloc(sizeof(Snode));
    if (!node) return NULL;
    node->data = n;
    node->next = make_single(n - 1);
    return node;
}

//Put the even nodes of head into first.
//Put the odd nodes of head in second.
void split_single(Snode *head, Snode **first, Snode **second)
{
    if (!head) return;
    Snode *f = head;
    Snode *s = head->next;
    if (s) {
        f->next = s->next;
        if (f->next) {
            s->next = f->next->next;
            split_single(f->next, NULL, NULL);
        }
    }
    if (first) *first = f;
    if (second) *second = s;
}

int main()
{
    Snode *list = make_single(12);
    print_single_list(list);
    Snode *first = NULL;
    Snode *second = NULL;
    split_single(list, &first, &second);
    print_single_list(first);
    print_single_list(second);
    return 0;
}

12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1
12, 10, 8, 6, 4, 2
11, 9, 7, 5, 3, 1