Walmart Senior Software Developer interview questions

Round1 : 1.Little bit discussion about previous projects. 2. Reason to use particular technologies in project. (like in my case why mongodb used) 3. Find unique pairs of sum in array of unsorted array. e.g - array a[]= [4,3,1,2,5] print pairs whose sum is 5. answer = (1,4), (2,3) 4. In Linked List, a node to be deleted. but in this i am not having refence of head node. I am having reference of that node which need to be deleted and order of linked list also remains same. e.g - linked list as 1 -> 2-> 3-> 4-> 5->null Node head reference is at 3 , not at first element, delete 3 from list. 5. What is Singelton Class in java? How to create ? 6. Internal working of Hashmap. Round 2 : 1. Detailed discussion about project. 2. If my server is capable of handling 10 requests at a time and 100 hits come together, how to handle in that case? 3. Binary Tree DS Questions - Find Height of tree 4. Level Order Traversal Of Binary Tree 5. What improvements you have brought in your project. 6. Name some of key challenges, which you fixed. Round 3 : 1. Little Discussion On Project. 2. Design Messenger System. 3. Stateful vs Stateless. 4. What is Caching? 5. How redis store data? Why you use it in your project. 6. Rest v/s Soap 7. Why Walmart?