Recursion | Linear Search | Find all indices | Lecture 33 | Java and DSA Course

 J     A     V     A              C     O     D      E

           1. Write a program to check  (x)  is exist or not in Array           

      </>    RecArrayExistenceCheck.java       

// METHOD (1) :
// FINDING  EXISTENCE  OF  AN  ELEMENT :

package Recursion;
import java.util.Scanner;

public class RecArrayExistenceCheck {
     public static void check(int []arr,int n,int x){
          if(arr[n]==x){
               System.out.println("YES");
               return ;
          }
          if(n==0){
               System.out.println("NO");
               return ;
          }
          check(arr,n-1,x);
     }
     public static void main(String[] args) {
          Scanner sc=new Scanner(System.in);
          System.out.println("Enter number of elements: ");
          int n=sc.nextInt();
          int []arr=new int[n];
          for(int i=0;i<n;i++)
               arr[i]=sc.nextInt();
          System.out.println("Enter which element you want to check :");
          int x=sc.nextInt();

          check(arr,n-1,x);

      sc.close();
     }
}
           2. Write a program to check  (x)  is exist or not in Array           
      </>    RecArrayExistByFreq.java       
// METHOD (2) :
// CHECKING  THE  EXISTENCE  OF  AN  ELEMENT  IN  AN  ARRAY :
// WE  DONE  IT  BY  THE  CONCEPT  OF  FREQUENCY  ARRAY :

package Recursion;
import java.util.Scanner;
public class RecArrayExistByFreq {
     public static void checkFreq(int []arr,int n,int x,int []freq){
          freq[arr[n]]++;
          if(n==0){
               if(freq[x]!=0) System.out.println("YES");
               else System.out.println("NO");
               return ;
          }
          checkFreq(arr,n-1,x,freq);
     }
     public static void main(String[] args) {
          Scanner sc=new Scanner(System.in);
          System.out.println("Enter number of elements in array: ");
          int n=sc.nextInt();
          int []arr=new int[n];
          for(int i=0;i<n;i++)
               arr[i]=sc.nextInt();
          System.out.println("Enter which element you want to check: ");
          int x=sc.nextInt();
          int []freq=new int [100005];
          checkFreq(arr,n-1,x,freq);


          sc.close();
     }
}
           3. Write a program to print at which index number that element is present          
      </>    RecArrayExistIndex.java       
// FINDING AT WHICH INDEX THAT ELEMENT EXIST :

package Recursion;
import java.util.Scanner;
public class RecArrayExistIndex {
     public static void check(int []arr,int n,int x,int key){

          if(arr[n]==x){
               System.out.println(x+" present at index : "+n);
               key=1;
          }
          if(n==0){
               if(key==0) System.out.println(-1);
               return ;
          }
          check(arr,n-1,x,key);
     }
     public static void main(String[] args) {
          Scanner sc = new Scanner(System.in);
          System.out.println("Enter no. of element : ");
          int n=sc.nextInt();
          int []arr=new int[n];
          for(int i=0;i<n;i++)
               arr[i]=sc.nextInt();
          System.out.println("Enter which element you want to check: ");
          int x=sc.nextInt();
          check(arr,n-1,x,0);

          sc.close();
     }
}
        4. Same as above Question BUT , In this the return type is ArrayList          
      </>    RecArrayListExistence.java       
// SAME  AS  ABOVE  QUESTION :
// NOW  THE  RETURN  TYPE  IS  ARRAY LIST :

package Recursion;
import java.util.Scanner;
import java.util.ArrayList;

public class RecArrayListExistence {
     public static ArrayList<Integer> checking(int []arr,int n,int x,int key,ArrayList<Integer>lst){
          if(arr[n]==x){
               lst.add(n);
               key=1;
          }
          if(n==0){
               if(key==0) System.out.println("NONE");
               return lst;
          }
          return checking(arr,n-1,x,key,lst);
     }
     public static void main(String[] args) {
          Scanner sc=new Scanner(System.in);

          System.out.println("Enter no. of elements: ");
          int n=sc.nextInt();
          int []arr=new int[n];
          for(int i=0;i<n;i++) arr[i]=sc.nextInt();

          System.out.println("Enter that element that you want to check: ");
          int x=sc.nextInt();

          ArrayList<Integer>lst=new ArrayList<>();
          ArrayList<Integer>ans=checking(arr,n-1,x,0,lst);

          System.out.println(ans);

          sc.close();
     }
}
        5. Write a program to check weather the Array is sorted or not           
      </>    RecArrayCheckSort.java       
// CHECKING  ARRAY  IS  SORTED  OR  NOT :

package Recursion;
import java.util.Scanner;

public class RecArrayCheckSort {
     public static void checkSort(int []arr,int n){
          if(arr[n]<arr[n+1]){
               if(n==0){
                    System.out.println("SORTED");
                    return ;
               }
          }
          else{
               System.out.println("NOT SORTED");
               return ;
          }
          checkSort(arr,n-1);

     }
     public static void main(String[] args) {
          Scanner sc=new Scanner(System.in);
          System.out.println("Enter no. of elements: ");
          int n=sc.nextInt();
          int []arr=new int[n];
          for(int i=0;i<n;i++) arr[i]=sc.nextInt();
          checkSort(arr,n-2);

          sc.close();
     }
}
        6. Write a program to check weather the element is exist or not           
      </>    RecArrayTarget.java       
// CHECKING  EXISTENCE OF  AN  ELEMENT  IN  AN  ARRAY :

package Recursion;
import java.util.Scanner;

public class RecArrayTarget {
     public static void check(int []arr,int n,int x){
          if(n==0){
               System.out.println("ELEMENT NOT EXIST");
               return ;
          }
          if(arr[n]==x){
               System.out.println("ELEMENT EXIST AT LAST INDEX : "+n);
               return ;
          }
          check(arr,n-1,x);
     }
     public static void main(String[] args) {
          Scanner sc=new Scanner(System.in);
          System.out.println("Enter number of elements: ");
          int n=sc.nextInt();
          int []arr=new int[n];
          for(int i=0;i<n;i++) arr[i]=sc.nextInt();
          System.out.println("Enter element that you want to check: ");
          int x=sc.nextInt();
          check(arr,n-1,x);

          sc.close();
     }
}
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