SDE - 1

Straight forward solution would be to use two pointers fast and slow.

I used two loops- first one to pick one value and subtract it from k ( k - first ) and the second nested loop to check whether any element equals to (k-first) 
This was not the optimized approach but essentially completeness was more important.

Head node was given , used three pointers previous , current and last and swapped them. 
Make sure to add null checks at all places. The editor would just allow you to run only test cases or custom cases but all other test cases (including hard ones ) were hidden.

Tip 1: try to remember all the layers using a trick like All Should Try New Dominos Pizza - Application Session Transport Data link Network Physical - it's important to list them down first 
Tip 2: Try to explain each layer and their role in detail

Tip 1: Call out significant difference and their use cases like data loss and acknowledgements availability 
Tip 2:What is difference between TCP/IP and UDP

Tip 1: I only knew full form and that HTTP uses TCP standard. 
Tip 2: Try to read RFCs/ documentation for this topic
Tip 3: Revise your networking concepts well

Tip 1: Keep it brief, everyone was exhausted by that time. 
 

Tip 1 : This was just for reference, They anyway gave gurgaon location to everyone from our college