Trying to implement k-medoids in C - c

Question

I am trying to implement an algorithm in C which splits a linked list. So what I am trying to do is, I have a linked list of all entries, I am trying to split that linked list into two separate lists based on distance of elements from a specific node.
What shiftAndCluster does is takes in a linked list list, 2 empty lists oldFreshList and newList and 2 nodes best1 and best2. It first searches for these 2 nodes in list and pushed them into 2 empty lists respectively. Then the function iterates over each node of list and calculates its distance from either of the nodes and pushes it to the list containing the closer best node.
The code goes like this
void shiftAndCluster(SinglyLinkedList* list, SinglyLinkedList* oldFreshList, SinglyLinkedList* newList, SinglyLinkedListNode *best1, SinglyLinkedListNode *best2)
{
SinglyLinkedListNode *curr1 = list->front;
SinglyLinkedList *temp = cloneFullList(list);
SinglyLinkedListNode *prev = curr1;
while (curr1 != NULL)
{
if (curr1 == best2)
{
break;
} //reach till best2 in the list, so we have the prev of best2 with us
prev = curr1;
curr1 = curr1->next;
}
if (prev == curr1)
{
list->front = curr1->next;
list->size--;
SinglyLinkedList_pushFront(newList,curr1);
}
else
{
prev->next = curr1->next;
list->size--;
SinglyLinkedList_pushFront(newList,curr1);
}
curr1 = list->front;
prev = curr1;
while(curr1 != NULL)
{
if (curr1 == best1) {
// break when found best1
break;
};
prev = curr1;
curr1 = curr1->next;
}
// first, middle and last
if (prev == curr1)
{
list->front = curr1->next;
list->size--;
SinglyLinkedList_pushFront(oldFreshList,curr1);
}
else
{
prev->next = curr1->next;
list->size--;
SinglyLinkedList_pushFront(oldFreshList,curr1);
}
int firstSize = 1;
int secondSize = 1;
curr1 = list->front;
double dist1, dist2;
while (curr1 != NULL && list->size)
{
curr1=list->front;
SinglyLinkedList_popFront(list);
dist1 = calculateDistance(curr1,best1);
dist2 = calculateDistance(curr1,best2);
if (dist1 < dist2)
{
SinglyLinkedList_pushFront(oldFreshList,curr1);
firstSize++;
if (firstSize == 10) break;
}
else
{
SinglyLinkedList_pushFront(newList,curr1);
secondSize++;
if (secondSize == 10) break;
}
}
list->front = temp->front;
list->size = temp -> size;
}
The size of list is 11 nodes so the algorithm stops when either of the new list reaches size 10. At the end, the old list is repopulated with it's original entries.
The struct has been defined as
typedef struct SinglyLinkedListNode
{
void *data;
struct SinglyLinkedListNode *next;
}SinglyLinkedListNode;
typedef struct SinglyLinkedList
{
int size;
struct SinglyLinkedListNode *front;
}SinglyLinkedList;
Helper functions are:
SinglyLinkedListNode* cloneList(SinglyLinkedListNode *head) {
if(head == NULL) return NULL;
SinglyLinkedListNode *result = (SinglyLinkedListNode *)malloc(sizeof(SinglyLinkedListNode));
result->data = head->data;
result->next = cloneList(head->next);
return result;
}
SinglyLinkedList* cloneFullList(SinglyLinkedList *list) {
if(list == NULL) return NULL;
SinglyLinkedList *result = (SinglyLinkedList *)malloc(sizeof(SinglyLinkedList));
result->size = list->size;
result->front = cloneList(list->front);
return result;
}
pushFront, popFront and calculateDistance functions are trivial and work correctly. (Can provide them if required, but I have tested them extensively, they work correctly)
The issue I am facing is that when I try to use this function in a loop, it breaks after a single iteration.
Example is
//templist is a normal linked list containing 11 nodes
SinglyLinkedListNode *ppp1 = templist->front;
SinglyLinkedListNode *ppp2 = templist->front;
int ctrin = 0, ctr=0;
while (ppp1 != NULL)
{
ctr++;
ppp2 = templist->front;
ctrin = 0;
while (ppp2 != NULL)
{
SinglyLinkedList* tp2 = createEmptyList();
SinglyLinkedList* np2 = createEmptyList();
ctrin++;
if (ppp1 == ppp2)
{
ppp2 = ppp2->next;
ctrin++;
}
shiftAndCluster(templist, tp2, np2, ppp1, ppp2, listType, 1);
templist = cloneFullList(list);
printf("(%d, %d)\n", ctr, ctrin);
ppp2 = ppp2->next;
}
iter++;
ppp1 = ppp1->next;
}
createEmptyList function just creates an empty list.
The output prints (1,2) indicating it does check for (1,1) and skip it and after shifting and clustering once, it breaks down. The incoming list is fine and I think there are issues with the logic of the function. Can someone please help?

Answer 1

May not be the only problem but when you do :
prev = curr1;
curr1 = curr1->next;
prev will always be different of curr1. So the test if (prev == curr1) if always false except if list->front is NULL