Linked list Midpoint

#1

I am printing the midpoint but nothing shows

void midPoint(Nodehead) {
Nodefast = head;
Node*slow = head;

while(fast->next != NULL || fast != NULL) {
	fast = fast->next->next;
	slow = slow->next;
}

Node*mid = slow;

cout << "Mid-Point is " << mid->data;

}

#2

The while loop condition must be:
while(fast != NULL && fast->next != NULL)
So change it and then check.

#3

@pratyush63 yes both the condition will true thanks it running fine but the things is when am setting the fast=head it will show nothing but when fast=head->next it will work.

I didn’t get this beacuse while fast reaches to null then it will also run fine

#4

Yes you can dry run this code considering both the cases (for even length linked list and odd length linked list).You will get the mistake.

#5

@pratyush63 yes i dry run this
let suppose we have 1->2->3->4
fast = head
slow = head
then fast will go the 3 element and the slow will 2 then fast = null also the slow 3 so it should return 3
after that condition will false .

#6

You code is running fine. You just have to change the conditions of the while loop to while(fast != NULL && fast->next != NULL)
Previously you had while(fast->next != NULL || fast != NULL)
You can notice here that when fast->next is Null but fast is not null, then the condition will be satisfied and the control will enter the loop. But inside the loop you perform fast = fast->next->next; You know that here fast->next is NULL so this statemnt will turn to fast=NULL->next and this will create the issue.You have to make sure that your code does not perform next of NULL anywhere.

#7

@pratyush63 okays I notice one this it will give we the segment fault when i interchanges both the condition like i did fast->next != NULL && fast !=NULL) why I think we can write both the condition is any order ?

#8

If you first keep fast->next != NULL in the condition this will cause segmentation fault. Consider a case when fast= NULL… so again in the loop condition fast->next is being performed which will give a segmentation fault. So the order must be (fast != NULL && fast->next != NULL
When the first condition is false in case of && ,the second condition is not checked…

Difference in conditions
#9

@pratyush63 thanku so much.
you clear my all of doubt i better understand the concepts .thanks for putting your great efforts: :slight_smile: