Recursion-7

Q1. Write a program to merge 2 strings alternately using recursion starting from the first input string.
i/p=abcd
efgh
o/p=aebfcg>h
import java.util.Scanner;
public class Test {
   public static void main(String[] args) {
       Scanner scn = new Scanner(System.in);
       System.out.println("Enter the first string: ");
       String a = scn.nextLine();
       System.out.println("Enter the second string: ");
       String b = scn.nextLine();
       System.out.print(merge(a, b));
       }
   public static String merge(String a, String b){
      String ans = "";
      if(a.length() == 0){
          ans += b;
          return ans;
      }
      if(b.length() == 0){
          ans += a;
          return ans;
      }
      ans += a.substring(0, 1);
      ans += b.substring(0, 1);
      ans += merge(a.substring(1, a.length()), b.substring(1, b.length()));
      return ans;
   }
}

Q2. Given a string, find its first uppercase letter and return the remaining substring, starting from the
uppercase letter.

Explanation=
Input: collegeWallah
Expected Output: Wallah

import java.util.*;
import java.util.Scanner;
public class Test{
        public static void main(String[] args){
             Scanner scn = new Scanner(System.in);
                System.out.println("Enter the input string: ");
                String s = scn.nextLine();
                System.out.println(rec(s, 0));
        }
        public static String rec(String s, int idx) {
                if(idx == s.length()) return "";
                if(Character.isUpperCase(s.charAt(idx))) return s.substring(idx);
                return rec(s, idx+1);
        }
}

Q3. Gicen a string` count total number of consonants in it. A consonant is an English alphabet character that is not cowel (a` e` i` o ani u). Examples of constants are b` c` i` f` ani g.
i/p=pwskills
o/p=7

import java.util.*;
import java.util.Scanner;
public class Test{
        public static void main(String[] args){
             Scanner scn = new Scanner(System.in);
                System.out.println("Enter the input string: ");
                String s = scn.nextLine();
                System.out.println(totalConsonants(s, s.length()));
        }
        public static int totalConsonants(String str, int n) {
            if (n == 1) {
                if(isconsonant(str.charAt(0)))
                    return 1;
                else
                    return 0;
            }
            if(isconsonant(str.charAt(n - 1)))
                return totalConsonants(str, n - 1) + 1;
            else
                return totalConsonants(str, n - 1);
        }
        public static boolean isconsonant(char ch){
            ch = Character.toLowerCase(ch);
            if(ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o' || ch == 'u'){
                return false;
            }
            return true;
        }
}

Q4. Gifen a string, return the number of lowercase characters in it using recursion.
i/p=CollegeWallah
o/p=11
import java.util.*;
import java.util.Scanner;
public class Test{
        public static void main(String[] args){
             Scanner scn = new Scanner(System.in);
                System.out.println("Enter the input string: ");
                String str = scn.nextLine();
                System.out.println(totallowercase(str, 0));
        }
        public static int totallowercase(String str, int idx) {
            if(idx == str.length()-1){
                if(str.charAt(idx) >= 97 && str.charAt(idx) <= 122){
                    return 1;
                }
                else{
                    return 0;
                }
            }
            if(str.charAt(idx) >= 97 && str.charAt(idx) <= 122){
                return totallowercase(str, idx+1) + 1;
            }
            else{
                return totallowercase(str, idx+1);
            }
        }
}
Q5. Given a string, recursively implement atoi() or Integer.parseInt() methou on it without actually using
the methou.
i/p=298
o/p=298
import java.util.*;
import java.util.Scanner;
public class Test{
        public static void main(String[] args){
             Scanner scn = new Scanner(System.in);
                System.out.println("Enter the input string: ");
                String str = scn.nextLine();
                System.out.println(rec(str, str.length()-1));
        }
        public static int rec(String str, int n) {
            if (n == 0) {
                return str.charAt(0) - '0';
            }
            return (rec(str, n - 1)*10 + str.charAt(n) - '0');
        }
}