100_day_code

There are two types of datatypes

1. primitive : The one which is already define in java

   • byte : 1 byte
     • ex:byte a = 5
   • short : 2 bytes
   • char : 2 bytes
     • ex:char b = 'A'
   • boolen : 1 byte
     • ex:boolean c = true
   • int : 4 bytes
   • long : 8 bytes
   • float : 4 bytes
   • double : 8 bytes

2. non-premitive : The one is made by us.

   • String
   • Array
   • Class
   • Object
   • Interface

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Type Conversion

Conversion happen when:

1. type compatible
2. destination type > source type

• Example: byte>short>int>float>long>double

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Type casting When we forcefully convert any number into any other datatype - float a = 19.0; - int b = (int) a;

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Operators

1. Arithmetic operators
   • Binary : + - * / %
   • Unary : ++ --
2. Relational operators
   • == != > < >= <=
3. logical operators
   • && || !
4. Bitwise operators
5. Assignment operators
   • = += -= *= /=

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Conditional Statement

1. if
2. else if
3. ternary operator
   • ex: int a = (5>4)?5:4;
4. Switch statement
   • ex: switch(condition){ case 1 : System.out.println("x"); break; case 2 : System.out.println("y"); break; case 3 : System.out.println("z"); break; default : System.out.ptintln("xyz"); }

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Loops

1. while
2. for loop
3. do while loop

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Functions in Java

1. parameters are after function name inside the ().

   • ex: public static void cal(int a int b)

2. When we define a function the parameters are know as formal parameters.

3. When we call the function the parameters are known as actual parameters.

4. Java always calls by value.

5. There are two types of function in Java

   • Inbuilt
     • ex: Math, nextInt(),...
   • Userdefined
     • ex: factor, sum,..

6. how can we do function overloadin in Java.

   • We can have to different formal parameters.
   • We can more formal parameters in different functions.

7. There are different types of scope in java

   • Function/method scope
     • ex: public static void sum(int a int b){ int sum= a+b; } public static void main(String args[]){ int a =10; }
   • block scope
     • ex: public static void main(String args[]){ for(int a=1; a<=2; a++){ System.out.println(a); } System.out.println(a); // THIS IS WRONG }

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Binary to Decimal

• Ex: 101 to 5

1 0 1 //Binary number 1(22) + 0(21) + 1(2*0) = 5 // This is how we can convert to Decimal number

while(bin<0){ int pow = 0; int dec = 0; last=bin%10; int dec = dec + (last*((Int)Math.Pow(2,pow))); pow++;

bin=bin/10;

}

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Decimal to Binary

• Ex: 7 to 111

2|7 - 1 //remainder 2|3 - 1 //remainder 2|1 - 1 //remainder 2|0

while(num<0){ int pow = 0; int dec= 0;

last = num%2;
int bin = dec + (last * ((int)Math.pow(10,pow)));
pow++;

num = num/2;

}

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Array in JAVA

List of element of same type which is placed in contiguous memeory is know as array.

1. Operation in Arrays

   • Create

     • ex: int example[] = new int[10];
     • ex: int example[] = {1,2,3};

   • Input

   • Output

   • Update

   • ex: input, output and update
     int marks[] = new int [50]; Scanner sc= new Scanner(System.in);

          marks[0] = sc.nextInt();
          marks[1] = sc.nextInt();
          marks[2] = sc.nextInt();
     
          System.out.println("length is" + marks.length);
          System.out.println("Phy " + marks[0]);
          System.out.println("Chem " + marks[1]);
          System.out.println("Math " + marks[2]);
     
          marks[2] = 98;
          System.out.println("Updated Math marks is " + marks[2]);
     
          int per = (marks[0]+marks[1]+marks[2])/3;
          System.out.println("Per is " + per + "%");
     

2. Linear search :

• Time complexicity in this algorithm is O(n). =>> Linear.java

3. Binary Search :

• Remeber the dictionary
• There is a mid, start and end which goes into a loop and finds out the key.
• The time complexity is log n. =>> Binary.java

4. prefix array:

• Take an example of max subarray sum
• Where in we need to create a prefix array rather then creatind a sub loops as a traditional method.
• formula: prefix[end]-prefix[start-1] =>> Subarrpre.java

5. Kadanes algorithm:

• When there is a negetive number in an Array and we need to find a sum of max subarray then suppose that all negetive numbers in the arrag are 0. =>> Kadanes.java

6. Trapping Rainwater algorithm:

• Find the total area of water trapped in the bar.
• Formula 1 : area = (waterlevel-barheight)*width
• Formula 2 : Waterlevel = min(maxL,maxR) =>> Tr.java

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Sorting algorithm

1. Bubble sort:

• The largest number in the array will come to the end by swapping the other element in the array. =>> Bubble.java

2. Selection sort:

• Pick the smallest element in from the array amnd push it to the beginning. =>> Selection.java

3. Insertion sort:

• Pick an element from unsorted part and put it in the right position in sorted part. =>> Insertion.java

4. Counting sort :

• We can use this shorting algo for small numbers where the array range can be big but the numbers in the array are small for example arr[] = {1,3,4,6,2,3,4,7,4,5}; arr[10] but range is 1 to 7; Count.java

5. Inbuilt sort function:

• Array.sort.(arr); also Array.sort.(arr,0,3); also is you want to convert into decending order then you need to use Array.sort(arr,Collection.reverseOrder());

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2D array

• There are rows and columns in 2D arrays.
• rows= horizontal direction and column= vertical direction.

1. Spiral matrix: Spiral.java
2. Diagonal sum: Diagonal.java
3. Sorted matrix: Sorted2d.java

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Strings

• Strigs are immutable.
• How do define string in Java
  • String str = "abc";
  • String str2 = new String("abc");
• If you want to compare two string we can have an object name Sting1.equals.Sting2
  • Ex: compstr.java
• There is a inbuilt sumction to find out the substring of any string variablename.substring(Start,End);
  • Ex: substr.java
• How to find largest string Lexicographically Ex: largeststr.java
• StringBuilder is a tool in Java that allows you to build and modify strings (words or sentences) efficiently. It’s like a set of building blocks where you can add, change, or remove pieces easily without creating a new set of blocks every time(Strings).

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Bit-wise operators

we need to remember the decimal to binary of 1 to 7 which is

• 0 - 000

• 1 - 001

• 2 - 010

• 3 - 011

• 4 - 100

• 5 - 101

• 6 - 110

• 7 - 111

• Binary AND &

  • 1 0 = 0
  • 0 1 = 0
  • 0 0 = 0
  • 1 1 = 1

• Binary OR |

  • 1 0 = 1
  • 0 1 = 1
  • 0 0 = 0
  • 1 1 = 1

• Bitwise XOR ^

  • 1 0 = 1
  • 0 1 = 1
  • 0 0 = 0
  • 1 1 = 0

• Bitwise one's complement ~

  • 0 = 1
  • 1 = 0
  • Rules for finding ~ complement
    • If the given number is 5 then the binary is 00000101.
    • The first bit is known as most significant bit and the last bit is know as least signinficant bit MSB LSB.
    • If the number at the begining is 1 then it is negitive numnber or else it is positive number.
    • Now do once complement which is 11111010.
    • Then add 1 to the complement.

• Bitwise left shift <<

  • Ex: For 5<<2 remove two bits from left move the remaining bits to left for 5 and add two 0's at the end of it.
  • Formula is a<< b = a*2^b.

• Bitwise right shift >>

  • Ex: For 6>>1 remove one bit from right move the remaining bits to right for 6 and add one 0 at the end of it.
  • Formula is a<< b = a*2^b.

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OOPS (object oriented programing)

• Object = They are entities in the real world.
• Class = They have entities of object.
  • Classes have different attributes(property) and functions(behaviour).
• Acces modifiers

  • public ex:

    public class Car{ public String colour;

      public void drive(){
          System.out.println("Driving");
      }
    

    }

  • private ex:

    public class Car{ private string colour;

      private void startengine(){
          System.out.println("Engine start");
      }
    
      public void drive(){
          startengin();
          System.out.println("Driving");
      }
    

    }

  • protected ex:

    public class Car{ protected String colour;

      protected void startengine(){
          System.out.println("Engine started");
      }
    

    } public class Sportcar extends car{ public void turbo(){ startengine(); System.out.println("Turbo active"); } }

  • default (also known as package-private)

• Constructor = It a special method which is invoked automatically at the time of object creation. There are three types of constructor. OOPS.java
  • Parameterised
  • Non perameterized
  • Copy constructor
    • Sallow constructor
    • Deep constructor
• When you call same types of constructor more then one time in the main function it is known as function overloading. Also know as Polymorphism.
• 4 Pillars of OOPS
  • Encapsulation = Wrapping of data and methods under a single unit. It also implements data hiding.
  • Inheritance Inheritance.java = When the properties and method of parent class is passed to child class. There are Types in inheritance as following:
    • Single level
    • Multi level
    • Hierarchial
    • Hybrid
  • Abstraction Abstract.java = Hiding all the unnecessary details and showing only the important parts to the user.
  • Polymorphism Polymorphism.java = When we do multiple work in a single form is known as polymorphism.
    • Compile time(Method overloading)
    • Run time(Method overriding)
• Interfaces Interface.java
  • All methods are public,abstract and without implementation.Used to achieve total abstraction
  • Used to achieve total abstraction.
  • Variables in the interface are final,public and static.
• Static keyword Static.java
  • Static keyword in java is used to share the same variable or method of a given class.
• Super keyword
  • super keyword is use to refer immediate parent class object.
• We can assign child object to parent variable.

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Recursion

• Recursion is a method of solving a computational problem where the solution depends on solution to smaller instances of the same problem.
• Always have a base case in recursion.

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Divide and conquer

• Merge short has a time complexity as inbuit short. Mergesort.java
  • First divide.
  • then mergeshort left part and right part.
  • then merge both left and right.
• Quick short it dosent take extra space as merge short. Quicksort.java
  • First thing is to find a pivot.
  • Do partition.
  • then call for quick short for left and right part.

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Time and Space complexity

• Time is function of n when we use normal case.
• For larger input size constant time algorithm is better then linear time code.
• For linear search and simple loop the time complexity is O(n).
• For nested loop the time complexity is O(n2).
• Time complexity for Binary search is O(logn).
• Merge short: if the value of n is divided by 2 (n/2) then the time taken is log2n.So the time cmplexicity of merge short is nlogn.
• For power function Time complexicity is O(n) ans space complexity is O(n).