Mid point Runner technique

#1

In this mid point runner technique, why we are taking fast pointer one step ahead of slow pointer instead both the pointers should starts from same position initially?

#2

@CODER_JATIN you can take as you will both will end by the same results. You will move O(1) already when you take faster ahead

#3

I didn’t understand . . . . .

#4

Hey @CODER_JATIN you have reopened you doubt. So what happens is, your slow as well as fast pointer starts from an initial position. your slow pointer does a jump of 1 step and fast pointer does a jump of 2 steps. So total distance covered by slow pointer is x and fast is 2x so when you do 2x-x you will get x as the mid point of the linked list

#5

ok check this link , https://ide.codingblocks.com/s/409969 , when i input linkedlist as (1 2 3 4) , then it should give output as 3 , but this code is giving output as 2 , why???

#6

It is giving output as 3 only, but it’s wrong. In even length linked list like as you mentioned in case of {1,2,3,4} the mid point is 2 only. if you want to show 3 then don’t do any changes keep it as this only. it will show 3 as an output.

node*middle(node*head)
{
    node*fast=head;
    node*slow=head;

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

    return slow;
}

But if you want to show 2 as the mid point of the linked list then in line number 3 of this code
make it as Node*fast=head->next;

Rest your code works fine for odd length of linked list

#7

jo bhaiya , abhi mera code hai usme agar mai input LINKEDLIST(1 2 3 4) enter karta hu to mid point 2 aa rha hai, to sahi hai vo?

#8

or agar mid point to 3 laana hai to initially fast ko ek steap ahead rakhna pdega i.e node*fast=head->next ???

#9

Yes

yes for even linked list[1,2,3,4] mid point is 2
for odd one both will work that is node*fast=head->next and node *fast=head
There’s a problem on leetcode for the same you can do that too in order to refine this concept.
In that problem if you have linked list of even length like [1,2,3,4] you have to print 3 in it. You can do that by doing this

#10

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