Cycle remove from linklist gives segmentfault - c++

Question

void removeLoop(Node* head)
{
// code here
// just remove the loop without losing any nodes
Node* rab=head;
Node* tur=head;
while(rab && rab->next)
{
rab=rab->next->next;
tur=tur->next;
if(tur==rab)
break;
}
Node* temp=NULL;
if(rab && rab->next)
{
rab=head;
while(rab!=tur)
{
rab=rab->next;
temp=tur;
tur=tur->next;
}
temp->next=NULL;
}
}
This is my code implemented using floyd algo.
Question link
https://practice.geeksforgeeks.org/problems/remove-loop-in-linked-list/1#
It is giving segment fault on submission not able to identify the particular test case it's failing
According to question no need to return anything.

Answer 1

If we take the input as
4
1 2 3 4
1
then it will show the segmentation error.
Reason: If you run the code on this specific testcase, then after running the first while loop, both tur and rab will point to the head of the list. Now the condition of while loop inside the if loop will always return false. And after that, the code on the next line temp->next=NULL will give error because temp was initially NULL and this line will exhibit undefined behavior.
The correct program should be:
void removeLoop(Node* head)
{
Node* rab=head;
Node* tur=head;
while (rab && rab->next) {
rab = rab->next->next;
tur = tur->next;
if (rab == tur)
break;
}
if (tur == rab)
{
tur = head;
if(tur == rab) {
while(rab->next != tur) rab = rab->next;
}
else {
while (tur->next != rab->next) {
rab = rab->next;
tur = tur->next;
}
}
rab->next = NULL;
}
}