Thread: Get the Union Set in Single Link List

hello everyone, i have a problem in blew program,i dont know how to get the union set without changing the head1. i want to put the union set in the head3.

Code:

/************************************************************************/
/*                Get the Union Set in Single Link List                 */
/************************************************************************/

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

typedef struct _tagLinkNode
{
    int data;
    struct _tagLinkNode *next;
}LinkNode;


LinkNode* CreateList(LinkNode *head)
{
    head = (LinkNode *)malloc(sizeof(LinkNode));
    if (NULL == head)
    {
        printf("malloc error\n");
        return;
    }
	head->data = 0;
	head->next = NULL;

	return head;
}

void InputData(LinkNode *head)
{
    LinkNode *p = NULL;
    LinkNode *pNode = NULL;
    int data = 0;

    p = head;

    scanf("%d", &data);

    while(-1 != data)
    {
        pNode = (LinkNode *)malloc(sizeof(LinkNode));
        if (NULL == pNode)
        {
            printf("malloc error\n");
            return;
        }
        if (-1 != data)
        {
            pNode->data = data;
            pNode->next = NULL;
            p->next = pNode;
            p = pNode;
        }
        scanf("%d", &data);
    }
}

void OutPutData(LinkNode *pHead)
{
    LinkNode *p = pHead;

    if (NULL != p)
    {
        p = p->next;
    }

    while (NULL != p)
    {
        printf("%d ", p->data);
        p = p->next;
    }
    printf("\n");
}

LinkNode** GetUnion(LinkNode *head1, LinkNode *head2, LinkNode **head3)
{
    LinkNode *p1 = head1;
    LinkNode *p2 = head2;
    LinkNode *p3 = NULL;
    LinkNode *p3pre = NULL;

    if (NULL == p1 && NULL == p2)
    {
        return;
    }

	head3 = (LinkNode **)malloc(sizeof(LinkNode));
	*head3 = (LinkNode *)malloc(sizeof(LinkNode));
	
	if (NULL == *head3 || NULL == head3)
	{
		printf("malloc error\n");
		return NULL;
	}

	(*head3)->data = 0;
	(*head3)->next = NULL;

    p1 = p1->next;
    p2 = p2->next;
    p3 = *head3 = head1;
    p3 = p3->next;

    while (NULL != p2)
    {
        p3pre = *head3;
        p3 = p3pre->next;
        while (NULL != p3)
        {
            if (p2->data == p3->data)
            {
                break;
            }
            p3pre = p3pre->next;
            p3 = p3->next;
        }
        if (NULL == p3)
        {
            p3pre->next = p2;
            p3pre = p3pre->next;
        }
        p2 = p2->next;
	}
	return head3;
}

int main()
{
    LinkNode *list1 = NULL;
    LinkNode *list2 = NULL;
    LinkNode **list3 = NULL;

    list1 = CreateList(list1);
    printf("please input single link list1(-1 end): ");
    InputData(list1);

	  list2 = CreateList(list2);
    printf("please input single link list2(-1 end): ");
    InputData(list2);

    printf("\n\nThe Set 1: ");
    OutPutData(list1);
    printf("The Set2: ");
    OutPutData(list2);

    //list3 = CreateList(list3);

    printf("The Union Set is :");
    list3 = GetUnion(list1, list2, list3);
    OutPutData(*list3);

    return 0;
}

If you can't solve a problem, divide it into smaller problems, try to first write a function to copy() a list and a function to concatenate() two existing lists without creating a new one.
Your getunion function will simply be a composition of those two functions.
You're talking about sets, if this last function must return a set then write a set() function that remove duplicated elements in a list.
Compose everything and you're done.

maybe i didn't express clearly, i mean, i want to use two single link list to get their union set. The "GetUnion" function has logical error but i dont know how to fix it.

i mean list 1: 1 2 3 4, list 2: 3 4 5 6, then the union set is 1 2 3 4 5 6

i've improved the GetUnion function.

Code:

LinkNode* GetUnion(LinkNode *head1, LinkNode *head2, LinkNode *head3)
{
    LinkNode *p1 = NULL;
    LinkNode *p2 = NULL;
    LinkNode *p3 = NULL;

    if (NULL != head1 && NULL != head2)
    {
		p3 = head3 = head1;
        p1 = head1->next;
		p2 = head2->next;
		p3 = p1;

		while (NULL != p1 && NULL != p2)
		{
			if (p2->data != p1->data)
			{
				if (NULL != p1->next)
				{
					p1 = p1->next;
				}
				else
				{
					p1->next = p2;
					p3 = p2;
					p1 = head1->next;
					p2 = p2->next;
					p3->next = NULL;
				}
			}
			else
			{
				p2 = p2->next;
				if (NULL != p2 && NULL == p3->next)
				{
					p3->next = p2;
				}
			}
		}
    }
	return head3;
}

may i still improve it?

im afraid of missing a '=' in the middle of if

Originally Posted by iMalc

You're using Yoda Conditions... Please don't.

Before I read that page, I half-expected Yoda Conditions to look like this:

Code:

if (DO || !DO) {
    // there is no try
}

Or like this:

Code:

if (x == 0) {
} else if (x != 0) {
}

By the way, I've recently seen the following if...else if pattern in production code at work:

Code:

if (0 == x) {
    // do something
} else if (0 != x) {
    // do something else
}

It's a double Yoda! The Force must be strong in this code.