Question

c++
using recursive
no loops  (for ,while ..ect)not allowed

Write a recursive function ‘bool palindrome(string s)’ that returns true if s is a palindrome and false if not.


#5: Write a recursive function 'void reverse(string &word)' that reverses the given input string.

string name = "damian";
reverse(name);
cout << name << endl;  //should display "naimad".



#7: Write a function 'int numTwos(int n)' which returns the number of 2's in the base-4 expansion of n.

cout << numTwos(2170) << endl; // 3

Answer 1

Check whether string is Palindrome or not code-

#include <iostream>
using namespace std;
bool isPalRec(string str, 
                        int s, int e) 
{ 

        if (s == e) 
        return true; 

        // If first and last characters do not match 
        if (str[s] != str[e]) 
        return false; 

        // If there are more than two characters, check if middle substring is also palindrome or not. 
        if (s < e + 1) 
        return isPalRec(str, s + 1, e - 1); 

        return true; 
} 

bool isPalindrome(string str) 
{ 
int n = str.length(); 

// An empty string is considered as palindrome 
if (n == 0) 
        return true; 

return isPalRec(str, 0, n - 1); 
} 

int main() 
{ 
        string str; 
        cin>>str;
        
        if(isPalindrome(str))
            cout<<"True";
        else
            cout<<"False";

        return 0; 
} 

Output

Reverse of string code

#include <iostream>
using namespace std;

void reverse_String(string& s, int n,int i){

  if(n<=i)
    return;

  swap(s[i],s[n]);
  reverse_String(s,n-1,i+1);

}

int main() {
  
  string str;
  cin>>str;
  int n= str.length();
  reverse_String(str,n-1,0);
  cout<<"reversed string is :"<<str;
  
}

Output

number of 2's in the base-4 expansion of n code-

#include <iostream> 
using namespace std; 

int base4(int n) 
{ 
 
        int rem,count=0; 

        int i = 0; 
        while (n > 0) { 
        rem = n % 4; 
                n = n / 4;
                if(rem==2)
                    count++;
        } 
        return count;
} 

int main() 
{ 
        int n;
        cin>>n;
        cout<<base4(n); 
        return 0; 
} 

Output

Recursive code

 
#include <bits/stdc++.h> 
using namespace std; 

int recusion_base4(int x) 
{ 
        if (x == 0) 
                return 0; 
        else
                return (x % 4 + 10 * recusion_base4(x / 4)); 
} 


int main() 
{ 
        int n;
        cin>>n;
        int ans= recusion_base4(n);
        int count=0;
        while(ans>0)
        {
            int rem=ans%10;
            ans= ans/10;
            if(rem==2)
                count++;
        }
        cout<<count;
        return 0; 
} 

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