Java Technical Blog

  Given the   root   of a binary tree,   check whether it is a mirror of itself   (i.e., symmetric around its center).   Example 1: Input: root = [1,2,2,3,4,4,3] Output: true Example 2: Input: root = [1,2,2,null,3,null,3] Output: false class Solution { public boolean isSymmetric(TreeNode root) { return isMirror(root.left, root.right); } public boolean isMirror(TreeNode t1, TreeNode t2) { if(t1==null && t2==null) return true; if(t1==null || t2==null) return false; return t1.val==t2.val && isMirror(t1.left, t2.right) &&                                     isMirror(t1.right, t2.left); } }

  Given the   root   of a binary tree,   determine if it is a valid binary search tree (BST) . A  valid BST  is defined as follows: The left subtree of a node contains only nodes with keys  less than  the node's key. The right subtree of a node contains only nodes with keys  greater than  the node's key. Both the left and right subtrees must also be binary search trees. Not a valid Binary tree as 4 is less than 5. Largest element in left subtree < root.val < Smallest element in left sub tree Binary Tree Inorder traversal gives sorted elements. Example 1: Input: root = [2,1,3] Output: true Example 2: Input: root = [5,1,4,null,null,3,6] Output: false Explanation: The root node's value is 5 but its right child's value is 4. To solve this we will apply Depth First Search. Code class Solution {     public TreeNode prev = null;     public boolean isValidBST(TreeNode root) {          ...

  Given the   root   of a binary tree, return   the inorder traversal of its nodes' values .   Example 1: Input: root = [1,null,2,3] Output: [1,3,2] Example 2: Input: root = [] Output: [] Example 3: Input: root = [1] Output: [1] class Solution { List<Integer> list = new ArrayList<Integer>(); public List<Integer> inorderTraversal(TreeNode root) { if(root==null) return new ArrayList<Integer>(); inorderTraversal(root.left); list.add(root.val); inorderTraversal(root.right); return list; } }

Given the  root  of a binary tree, return  its maximum depth . A binary tree's  maximum depth  is the number of nodes along the longest path from the root node down to the farthest leaf node.  Example 1: Input: root = [3,9,20,null,null,15,7] Output: 3 Example 2: Input: root = [1,null,2] Output: 2 class Solution { public int maxDepth(TreeNode root) { if(root==null) return 0; int d1 = maxDepth(root.left); int d2 = maxDepth(root.right); return Math.max(d1,d2)+1; } } Explanation 1. Calculate the depth of the left subtree and right tree. 2. Get max of left and right sub tree. 3. Depth of tree is max + 1 as include root node also. 4. Base condition is root is null then return 0.

The CAP theorem, or Brewer’s theorem, is a fundamental theorem within the field of system design. It was first presented in 2000 by Eric Brewer, a computer science professor at U.C. Berkeley, during a talk on principles of distributed computing. In 2002, MIT professors Nancy Lynch and Seth Gilbert published a proof of Brewer’s Conjecture. The CAP theorem states that a distributed system can only provide two of three properties simultaneously: consistency, availability, and partition tolerance. The theorem formalizes the tradeoff between consistency and availability when there’s a partition. A distributed system is a collection of computers that work together to form a single computer for end users. All of the distributed machines have one shared state and operate concurrently. With distributed systems, users must be able to communicate with any of the distributed machines without knowing it’s only one machine. The distributed system network stores its data on more than just a single no...

 SQL Function Vs Procedure View Vs Materialised View View:  View is just a named query. It doesn't store anything. When there is a query on view, it runs the query of the view definition. Actual data comes from table. Materialised views:  Stores data physically and get updated periodically. While querying MV, it gives data from MV.

 WeakHashMap WeakHashMap is an implementation of the Map interface. WeakHashMap is almost same as HashMap except in case of WeakHashMap, if object is specified as key doesn’t contain any references- it is eligible for garbage collection even though it is associated with WeakHashMap. i.e Garbage Collector dominates over WeakHashMap. Private method in interface After Java 9, we can have private method in interface. Spring Propagation While dealing with Spring managed transactions the developer is able to specify how the transactions should behave in terms of propagation. In other words the developer has the ability to decide how the business methods should be encapsulated in both logical or physical transactions. Methods from distinct Spring beans may be executed in the same transaction scope or actually being spanned across multiple nested transactions. This may lead to details like how does the inner transaction outcome result affects the outer transactions. REQUIRED behavior ...

We have all watched trees from our childhood. It has roots, stems, branches and leaves. It was observed long back that each leaf of a tree can be traced to root via a unique path. Hence tree structure was used to explain hierarchical relationships, e.g. family tree, animal kingdom classification, etc. This hierarchical structure of trees is used in Computer science as an abstract data type for various applications like data storage, search and sort algorithms. A tree is a hierarchical data structure defined as a collection of nodes. Nodes represent value and nodes are connected by edges. A tree has the following properties: The tree has one node called root. The tree originates from this, and hence it does not have any parent. Each node has one parent only but can have multiple children. Each node is connected to its children via edge. Terminology 1. Root is a special node in a tree. The entire tree originates from it. It does not have a parent. 2. Parent node is an immediate predecess...

 Load Vs Get load() get() Only use  load()  method if you are sure that the object exists. If you are not sure that the object exist, then use one of  get()  methods. load()  method will throw an exception if the unique id is not found in the database. get()  method will return null if the unique id is not found in the database. load()  just returns a proxy by default and database won't be hit until the proxy is first invoked. get()  will hit the database immediately.

Trie is an efficient information reTrieval data structure. Using Trie, search complexities can be brought to optimal limit (key length). If we store keys in binary search tree, a well balanced BST will need time proportional to M * log N, where M is maximum string length and N is number of keys in tree. Using Trie, we can search the key in O(M) time. However the penalty is on Trie storage requirements. Every node of Trie consists of multiple branches. Each branch represents a possible character of keys. We need to mark the last node of every key as end of word node. A Trie node field isEndOfWord is used to distinguish the node as end of word node. A simple structure to represent nodes of the English alphabet can be as following,  // Trie node  struct TrieNode  {       struct TrieNode *children[ALPHABET_SIZE];      // isEndOfWord is true if the node       // represents end of a word       bool isEn...

What is Cloud Computing? Cloud computing is the on-demand delivery of compute power, database storage, applications, and other IT resources through a cloud services platform via the internet with pay-as-you-go pricing. AWS Shared Responsibility Model AWS responsibility “Security of the Cloud” - AWS is responsible for protecting the infrastructure that runs all of the services offered in the AWS Cloud. This infrastructure is composed of the hardware, software, networking, and facilities that run AWS Cloud services. Customer responsibility “Security in the Cloud” - Customer is responsible for everything that goes IN the cloud (data, encryption, IAM, software, etc.) It is crucially important to understand which components and parts of AWS are your responsibility for each service. For example, with EC2 you maintain control over the OS, whereas with RDS, AWS is responsible for the OS. The Shared Responsibility model will show up heavily on the exam. Additional details are available on the A...

 git version git config --global user.name "Abe Lincoln" git config --global user.email "mrabe@git.training" git config --global --list git clone github-https-url # paste in your GitHub HTTPS clone URL ls cd github-demo ls git status echo "Test Git Quick Start demo" >> start.txt ls cat start.txt git status git add start.txt git status git commit -m "Adding start text file" git status git push origin master

  What is Distributed Tracing ? One of the major challenges in microservices is the ability to debug issues and monitor them. A simple action can trigger a chain of microservice calls and it would be tedious to trace these actions across the invoked microservices. This is because each microservice runs in an environment isolated from other microservices so they don’t share resources such as databases or log files. In addition to that, we might also want to track down why a certain microservice call is taking so much time in a given business flow. The Distributed Tracing pattern addresses the above challenges developers face while building microservices. There are some helpful open-source tools that can be used for distributed tracing, when creating microservices with Spring Boot and Spring Cloud frameworks. This blog walks through the installation steps and implementations of these tools. Spring Cloud Sleuth: A Spring Cloud library that lets you track the progress of subsequent mic...