Concepts of Computer Science

when someone starts a career in software engineering there are plenty of options. Although most graduates have the same degree, everyone starts in a different role. Developer / Coder - Engineers in this role get a chance to actually implement and write software. At the start of a career mostly it is about fixing defects in existing software then taking small changes to the software and eventually getting to the point to handle and implement more complex changes.  Quality analysts / Quality engineers - Engineers in this role test and automate software. This is a challenging role where one has to know about the full functionality of the software and test accurately so the software built is of high quality. This role also involves the automation of test cases and preparing a test suite that can be run and detect issues automatically. Release Engineers - Once the software is built and tested release engineers are responsible for pushing a set of code to production. A production is a ...

Here is a list of some of the best questions asked in interviews Must do Top interview questions Top 100 liked Must do 75  Must do 60  Must do medium Data structures Tree Graph  Dynamic Programming Company Interviews FaceBook interviews Amazon Interviews Google Interviews Github master List

  A message containing letters from   A-Z   is being encoded to numbers using the following mapping: 'A' -> 1 'B' -> 2 ... 'Z' -> 26 Given a  non-empty  string containing only digits, determine the total number of ways to decode it. Example 1: Input: "12" Output: 2 Explanation:  It could be decoded as "AB" (1 2) or "L" (12). Example 2: Input: "226" Output: 3 Explanation:  It could be decoded as "BZ" (2 26), "VF" (22 6), or "BBF" (2 2 6). class Solution { public int numDecodings(String s) { int ways=0; ways=countDecoding(s.toCharArray(),s.length()); return ways; } int countDecoding(char[] digits, int n){ // System.out.println(" digits "+disgits[0]); // for base condition "01123" should return 0 // base cases if (n == 0 || (n == 1 && digits[0]!='...

  Given two words  word1  and  word2 , find the minimum number of operations required to convert  word1  to  word2 . You have the following 3 operations permitted on a word: Insert a character Delete a character Replace a character Example 1: Input: word1 = "horse", word2 = "ros" Output: 3 Explanation: horse -> rorse (replace 'h' with 'r') rorse -> rose (remove 'r') rose -> ros (remove 'e') Solution:- class Solution { public int minDistance(String word1, String word2) { if(word1.length()==0){ return word2.length(); } if(word2.length()==0){ return word1.length(); } if(word1.length()==0 && word2.length()==0){ return 0; } int[][] result=new int[word1.length()+1][word2.length()+1]; for(int i=0;i<=word1.length();i++){ result[i][0]=i; } ...

   https://leetcode.com/problems/two-sum/ Given an array of integers  nums  and an integer  target , return  indices of the two numbers such that they add up to  target . You may assume that each input would have  exactly  one solution , and you may not use the  same  element twice. You can return the answer in any order.   Example 1: Input: nums = [2,7,11,15], target = 9 Output: [0,1] Output: Because nums[0] + nums[1] == 9, we return [0, 1]. Example 2: Input: nums = [3,2,4], target = 6 Output: [1,2] Example 3: Input: nums = [3,3], target = 6 Output: [0,1] class Solution {     public int[] twoSum(int[] nums, int target) {              HashMap<Integer,Integer> map=new HashMap<Integer,Integer>();                  for(int i=0;i<nums.length;i++){                      ...

user storage:- it can be solved using same scenario as mentioned in first article . https://tech.nazarmubeenworks.com/2019/08/basics-of-system-design-chapter-0.html Suppose there are 12 Million of users are adding every year meaning 1 Million per month. So if we consider 5 year there will be around 60 million of users. Now in terms of data we can look to our DB table and get information about it. A user will be generally having name , id , address , some forien keys . Lets assume 10 columns with each column on an average storing 4 byte of data. 10*4 = 40 bytes of data for one user. 60 * 10^6 * 40 = 2400 * 10^6 = 2.4 * 10^9 = 2.4 GB of data we need to store only user values. Also while calculating storage for the user there is also one important point we need to remember is of ids. If we are going to have 60 Million of users which means 60*10^6 users so unique id’s will be as we know below figures are almost equal ...

This article is first one from the series of articles dedicated to system design interviews. Here i am going to present the base scenario to consider before starting to solve system design problems. Questions to ask? 1) what is the number of requests a website will recieve in a day/month/second? 2) what is the amount of memory a website will deal in a day/month/second? 3) what is the number of servers that can accomodate these requests? To answer this , first we need to remember the below numbers:- 1 million = 10 lakh = 1000000 = 10^6 1 billion = 1000 million = 10^9 1 KB = 1024 B = 10^3 1 MB= 10^6 = 1024 KB 1 GB= 10^9 = 1024 MB 1 TB = 10^12 = 1024 GB Memory we need to see in Bytes Requests we need to see in numbers example :- suppose a website recieves 100M requests every month then:- requests per day = request per month /24 = 416700 requests requests per second = requests per day / (24*360...

Learn in a different way :- Strings stacks and queues heaps searching hash table sorting recursion dynamic programming greedy algorithms graphs tree Binary Search Tree Linked List Array Parallel programming and concurrency design problems system design availability and scalability  Below topics are good to have object oriented programming language details ( java , python) object oriented design tools ( bash , git , maven , jira , jenkins , docker , kubernetes) database

There is no secret to doing effective programming but following a sequence of steps and procedures can help in building great programs. Today I will take you on a tour to some of the best practices that are integrants of perfect programs. Algorithms are important: - You can’t deny the fact that algorithms are important and before start to write any program, Algorithms are must to write. For example, if there is a program about finding the sum of two numbers? What will you write ?The steps can be :- 1)   Get the first number. 2)   Get the second number. 3)   Add both numbers. This is what algorithm is writing about ,a list of statements .From the above three statements you can conclude boundary cases (at least two number should be there in input), mathematical function(Sum is needed here) , storage capacity(amount of memory to be assign to the variables), number of methods by analyzing repeat steps (reduce replete codes) and many other things. During alg...

Left Rotation in an Array using Java There are two methods implemented by me here :- 1) Using extra Array   Get new position of  a current element using formula.  Add the element in the new position in a new array. 2) Using same Array:- This is little bit complex hold variable at index i. find new index for variable. hold variable present at new index. place variable at index i to this new index. assign i to new index variable. repeat steps until count is not equal to lenght of an array which simply means all variable got covered. package Arrays ; /* * 12345 to 34512 */ /* * sample input * 5 4(d=4 that is 4 rotations) 1 2 3 4 5 sample output 51234 */ public class LeftRotation { public static void printArray ( int [] arr ) { for ( int i =0; i < arr . length ; i ++) { System . out . print ( " " + arr [ i ]); } System . out . println ( " " ); } //method ...

Difference between Abstract Class and Interface Difference between abstract class and interface ? Abstract Class:- 1) Can have abstract and non-abstract method both. 2) One class can extend at most one class. 3) can declare non abstract method and also can define body for it. Interface:- 1) can have only abstract method. 2) One class can implement multiple interfaces. 3) can't delare body to a method. Please look below example for more understanding:- package Basics ; public abstract class Animal { int head ; //no body (unimplemented function need to override in child class as a //compulsion abstract void setLegs (); //having body //may override or may not void setHead () { head =1; } } package Basics ; // can have only methods and by default all are abstract need to be override //by implementing class, unlike abstract no method can havedefinition public interface Pet { void tellWhereAreYouFr...

Basics of java in layman term for beginner What is an object ? object is a real world entity. Object is an instance of the class.It means something that is alive. Let us take an example of CAR:- concept of a car is class. I mean we all know that it is having four tyres , one engine , four doors , a seat e.t.c. but we can't do anything just by the concept we need real Car to perform operations on it . This real car is what we call is an object. Explain about main() method in java ? main() method is an entry point of a program. public static void main(String[] args) Why main() method is public, static and void in java ? public: It can be accessed from anywhere. static: no class object need to call this method. void: it is not returning anything in back. What is JIT compiler ? JIT is just in time compiler.JIT compiler runs after the program has started and compiles the code (usually bytecode or some kind of VM instructions) on the fly (or just-...