Queue, priority queue -> delete from mid,time, dequeue Avl tree, dfs tree ,time complexity, binary tree -> dfs /bfs when to use? Is tree a graph or vice a versa Queue implement using stack Reverse stack ,Kadane algo, Fibonacci series hashmap-> explain, collisions in hashmap, time to access Array find min without sort(), heap sort Graph shortest path find -> algo djikstra, bellman ford, floyd warshall diffrences https://www.geeksforgeeks.org/puzzle-19-poison-and-rat/ https://www.geeksforgeeks.org/puzzle-8-balls-problem/ Drop delete truncate, if 2 table connected and we drop table2 what happen to table1 Sql to find 6th salary, sql query to get 2nd highest salary Joins (inner,outer, left,right)+example , indexes, Primary key Polymorphism, types of poly, data abstraction, method overloading, overriding Acid properties , super and this difference , singleton class