recursion2.java

import java.util.*;

public class recursion2 {
    public static void towerOfHanoi(int n, String src, String helper, String dest){
        if (n==1){
            System.out.println("transfer disk "+ n +"from "+ src +"to "+dest);
            return;
        }
        towerOfHanoi(n-1,src,dest,helper);
        System.out.println("transfer disk "+ n+"from "+src+"to "+dest);
        towerOfHanoi(n-1, helper, src, dest);
  }
  public static void reverseString(int idx, String str){
    if(idx==0){
        System.out.println(str.charAt(idx));
        return;
    }

    System.out.print(str.charAt(idx));
    reverseString(idx-1, str);
   
  }
  public static int f=-1,l=-1;
  public static void faloccur(String str, int idx,char element){
    if (idx==str.length()){
        System.out.println(f);
        System.out.println(l);
        return;
    }
    char current=str.charAt(idx);
    if (current==element){
        if(f==-1){
            f=idx;
        }else{
            l=idx;
        }
    }   
    faloccur(str, idx+1, element);     
  }
  //check if array is sorted
  public static boolean isSorted(int arr[], int idx){
    if(idx==arr.length-1){
        return true;
    }
    if(arr[idx]<arr[idx+1]){
        //array is sorted till now
        return isSorted(arr, idx+1);
    }else{
        return false;
    }
  }
  public static void moveAllX(String str1,int idx,int count,String newString){
    if (idx==str1.length()){
        for (int i=0;i<count;i++){
            newString+='x';
        }
        System.out.println(newString);
        return;
    }
    char current=str1.charAt(idx);
    if(current=='x'){
       count++;
       moveAllX(str1, idx+1, count, newString);
    }else{
        newString+=current;
        moveAllX(str1, idx+1, count, newString);
    }
  }
  //remove duplicates from the string
  public static boolean map[]=new boolean[26];
  public static void removeDup(String str2,int idx, String newString1){
    if (idx==str2.length()){
        System.out.println(newString1);
        return;
    }
    char current=str2.charAt(idx);
    if (map[current-'a']){
        removeDup(str2, idx+1, newString1);
    }else{
        newString1+=current;
        map[current-'a']=true;
        removeDup(str2, idx+1, newString1);
    }
  }

    public static void main(String args[]){
    Scanner sc =new Scanner(System.in);
    int n=sc.nextInt();
    towerOfHanoi(n, "S", "H", "D");
    String str="abaacdaefaah";
    int idx=str.length()-1;
    reverseString(idx, str);
    faloccur(str, 0, 'a');
    int arr[]={1,2,3,4,5};
    System.out.println(isSorted(arr, 0));
    String str1="axbcxxd";
    moveAllX(str1, 0, 0, "");
    String str2="aabcadb";
    removeDup(str2, 0, "");
    }
    
}