40 Most important Java interview questions topic wise:
Question 1: Implement a stack using array.
Question 2: Implement a stack using Linked List :
Question 3: Implement a stack using two queues .
Question 4 : Sort an stack using another stack
Linked List :
Question 5 : Implement singly linked list in java.
Question 6: How to reverse linked list in java.
Question 7: How to find middle element of linked list.
Question 8 : How to find nth element from end of linked list .
Question 9 : How to detect a loop in linked list. If linked list has loop, find the start node for the loop.
Question 10: How to check if linked list is palindrome or not?
Question 11 : How to reverse a linked list in pairs?
Binary Tree :
Question 12: How can you traverse binary tree?
Question 13 : Write an algorithm to do level order traversal of binary tree?
Question 14 : Write an algorithm to do spiral order traversal of binary tree?
Question 15: How can you print leaf nodes of binary tree?
Question 16: How to count leaf nodes of binary tree.
Question 17. How to print all paths from root to leaf in binary tree.
Question 18 : How to find level of node in binary tree
Question 19: How to find maximum element in binary tree.
Question 20 : How to find lowest common ancestor(LCA) in binary tree.
Question 21 : How to do boundary traversal of binary tree.
Question 22 : How to print vertical sum of binary tree?
Binary Search tree:
Question 23 : What is binary search tree?
Question 24: Can you write algorithm to insert a node in binary search tree.
Question 25: Can you write algorithm to delete a node in binary search tree.
Question 26: How can you find minimum and maximum elements in binary search tree?
Question 27 : How to find lowest common ancestor(LCA) in binary search tree.
Question 28 : Can you write algorithm for merge sort and also do you know complexity of merge sort?
Question 29 : What is binary search? Can you write an algorithm to find an element in sorted array using binary search?
Question 30 : Find missing number in the array.
Question 31 : Search an element in rotated and sorted array.
Question 32: Find second largest number in an array
Question 33: Find the number occurring odd number of times in an array
Question 34: Find minimum number of platforms required for railway station
You are given arrival and departure time of trains reaching to a particular station. You need to find minimum number of platforms required to accommodate the trains at any point of time.
Question 35: Find a Pair Whose Sum is Closest to zero in Array
Question 36: Given a sorted array and a number x, find the pair in array whose sum is closest to x
Question 37: Find all pairs of elements from an array whose sum is equal to given number
Question 38 : Write algorithm to do depth first search in a graph.
Question 39: Write algorithm to do breadth first search in a graph.
Question 40 : What is an algorithm and how to calculate complexity of algorithms.