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Recursive program to replace all occurrences of pi with 3.14 in a given string
  • Difficulty Level : Medium
  • Last Updated : 11 Jun, 2021

Given string str of size N. The task is to write a recursive function to replace all occurrences of pi with 3.14 in the given string and print the modified string.

Examples: 

Input : str = “pippppiiiipi” 
Output : 3.14ppp3.14iii3.14

Input : str = “pip” 
Output : 3.14p

Input : str = “xpix” 
Output : x3.14x



We have discussed an iterative function here
Approach :  

  • If there is only one character in a string or the string is empty break the recursive call
  • Else keep the first character of the string with yourself and pass the rest of the string to recursion. 
    • If the first character is not ‘p’ then just put that character in front of the answer which came from recursion
    • Else if the first character is ‘p’ and the first character of the part passed to recursion is ‘i’ then replace “pi” with “3.14”

Below is the implementation of the above approach:

C++




// A recursive C++ program to replace
// all pi in a given string with 3.14
#include <bits/stdc++.h>
using namespace std;
 
// Recursive Function to replace all
// occurrences of pi in a given
// with 3.14
void replacePiHelper(char str[], int start)
{
 
    // Base condition
    // if the string is empty
    // or of length one
    if (str[start] == '\0' || str[start + 1] == '\0') {
        return;
    }
 
    // Getting the answer from
    // recursion for the smaller
    // problem
    replacePiHelper(str, start + 1);
 
    // Small calculation part
    // if the first character is 'p'
    // and the first character of the part
    // passed to recursion is 'i' then replace
    // "pi" with "3.14"
    if (str[start] == 'p' && str[start + 1] == 'i') {
 
        // Shifting the characeters to
        // right side to put 3.14 in
        // the character array
        for (int i = strlen(str); i >= start + 2; i--) {
            str[i + 2] = str[i];
        }
 
        // Replacing with "3.14"
        str[start] = '3';
        str[start + 1] = '.';
        str[start + 2] = '1';
        str[start + 3] = '4';
    }
}
 
// Function to replace pi with 3.14
void replacePi(char str[])
{
    replacePiHelper(str, 0);
}
 
// Driver code
int main()
{
    char str[] = "pippppiiiipi";
 
    // Function call
    replacePi(str);
 
    cout << str;
 
    return 0;
}

Java




// A recursive Java program to replace
// all pi in a given string with 3.14
 
class GFG {
 
    // Recursive Function to replace all
    // occurrences of pi in a given
    // with 3.14
    public String replacePi(String str)
    {
        // base condition
        // if the string is empty
        // or of length one
        if (str.length() <= 1) {
            return str;
        }
 
        // if the first character is 'p'
        // and the first character of the part
        // passed to recursion is 'i' then replace
        //"pi" with "3.14"
        if (str.charAt(0) == 'p' && str.length() >= 2
            && str.charAt(1) == 'i') {
            return "3.14" + replacePi(str.substring(2, str.length()));
        }
 
        // if the first character is not 'p'
        // then just put that character in
        // front of the answer which came
        // from recursion
        return str.charAt(0) + replacePi(str.substring(1, str.length()));
    }
 
    // Driver Code
    public static void main(String args[])
    {
        GFG g = new GFG();
        String str = "pippppiiiipi";
        System.out.println(g.replacePi(str));
    }
}

Python3




# A recursive Python3 program to replace
# all pi in a given string with 3.14
 
# Recursive Function to replace all
# occurrences of pi in a given
# with 3.14
def replacePieHelper(string, start):
 
    # Base condition
    # if the string is empty
    # or of length one
    if len(string) < 2 or start == len(string):
        return string
 
    # Getting the answer from
    # recursion for the smaller
    # problem
    replacePieHelper(string, start + 1)
 
    # Small calculation part
    # if the first character is 'p'
    # and the first character of the part
    # passed to recursion is 'i' then replace
    # "pi" with "3.14"
    if(string[start] == 'p' and
       string[start + 1] == 'i'):
 
        # Replacing with "3.14"
        string[start:start + 2] = ['3', '.', '1', '4']
 
# Function to replace pi with 3.14
def replacePi(string):
    replacePieHelper(string, 0)
 
# Driver Code
if __name__ == "__main__":
    string = "pippppiiiipi"
 
    string = list(string)
 
    # Function call
    replacePi(string)
 
    string = ''.join(string)
    print(string)
 
# This code is contributed by
# sanjeev2552

C#




// A recursive C# program to replace
// all pi in a given string with 3.14
 
using System;
class gfg {
    // Recursive Function to replace all
    // occurrences of pi in a given
    // with 3.14
    public String replacePi(String str)
    {
        // base condition
        // if the string is empty
        // or of length one
        if (str.Length <= 1) {
            return str;
        }
 
        // if the first character is 'p'
        // and the first character of the part
        // passed to recursion is 'i' then replace
        //"pi" with "3.14"
        if (str[0] == 'p' && str.Length >= 2
            && str[1] == 'i') {
            return "3.14" + replacePi(str.Substring(2, str.Length - 2));
        }
 
        // if the first character is not 'p'
        // then just put that character in
        // front of the answer which came
        // from recursion
        return str[0] + replacePi(str.Substring(1, str.Length - 1));
    }
}
 
// Driver Code
class geek {
    public static int Main()
    {
        gfg g = new gfg();
        string input = "pippppiiiipi";
        Console.WriteLine(g.replacePi(input));
        return 0;
    }
}

Javascript




<script>
 
      // A recursive JavaScript program to replace
      // all pi in a given string with 3.14
       
      // Recursive Function to replace all
      // occurrences of pi in a given
      // with 3.14
      function replacePi(str) {
        // base condition
        // if the string is empty
        // or of length one
        if (str.length <= 1) {
          return str;
        }
 
        // if the first character is 'p'
        // and the first character of the part
        // passed to recursion is 'i' then replace
        //"pi" with "3.14"
        if (str[0] === "p" && str.length >= 2 && str[1] === "i") {
          return "3.14" + replacePi(str.substring(2, str.length));
        }
 
        // if the first character is not 'p'
        // then just put that character in
        // front of the answer which came
        // from recursion
        return str[0] + replacePi(str.substring(1, str.length));
      }
 
      // Driver Code
      var input = "pippppiiiipi";
      document.write(replacePi(input));
       
</script>
Output
3.14ppp3.14iii3.14

Another Approach:

A simple recursive approach to replace all pi in a given function with “3.14”. Firstly function is declared we don’t need any helper function.

  • Base case if the string is empty or the length of the string is 1 return the string.
  • If the 0th and 1st element of the string is p and we have to handle them for the rest we have to call recursion it will give the result.
  • If not then we have to call recursion from 1st to all elements then add recursion result to 1st element and return it.

Below is the implementation of the above approach:

C++




// C++ program for above approach
#include <bits/stdc++.h>
using namespace std;
 
// A simple recursive approach
// to replace all pi in a given
// function with "3.14". Firstly
// function is declared we don't
// need any helper function one
// function is enough
string replacePi(string s)
{
 
    // Base case if s is empty
    // or length of s is 1
    // return the s
    if (s.length() == 0 || s.length() == 1)
        return s;
 
    // If the 0th and 1st element
    // of s are p and i we have to
    // handle them for rest we have
    // to call recursion it will
    // give the result
    if (s[0] == 'p' && s[1] == 'i') {
 
        // Smalloutput is a variable
        // used to store recursion result
        string smallOutput = replacePi(s.substr(2));
 
        // And we have to add the recursion
        // result with the first part we
        // handeled and return the answer
        return "3.14" + smallOutput;
    }
    else {
        // If 1st & 2nd element aren't "p" & "i", then keep
        // 1st index as it is & call recursion for rest of
        // the string.
        return s[0] + replacePi(s.substr(1));
    }
}
 
// Driver code
int main()
{
    string s = "pipppiiipi";
 
    // Function call
    string result = replacePi(s);
 
    cout << result << endl;
 
    return 0;
}
 
// This code is contributed by divyeshrabadiya07

Java




// Java program for above approach
class GFG {
 
    // A simple recursive approach
    // to replace all pi in a given
    // function with "3.14". Firstly
    // function is declared we don't
    // need any helper function one
    // function is enough
    public static String replacePi(String s)
    {
 
        // Base case if s is empty
        // or length of s is 1
        // return the s
        if (s.length() == 0 || s.length() == 1)
            return s;
 
        // If the 0th and 1st element
        // of s are p and i we have to
        // handle them for rest we have
        // to call recursion it will
        // give the result
        if (s.charAt(0) == 'p' && s.charAt(1) == 'i') {
 
            // Smalloutput is a variable
            // used to store recursion result
            String smallOutput = replacePi(s.substring(2));
 
            // And we have to add the recursion
            // result with the first part we
            // handeled and return the answer
            return "3.14" + smallOutput;
        }
        else {
 
            // If not then we have to call
            // recursion from 1st to all elements
            // then add recursion result to
            // 1st element and return it
            String smallOutput = replacePi(s.substring(1));
            return s.charAt(0) + smallOutput;
        }
    }
 
    // Driver code
    public static void main(String[] args)
    {
        String s = "pipppiiipi";
 
        // Function call
        String result = replacePi(s);
        System.out.println(result);
    }
}
 
// This code is contributed by divyesh072019

Python




# Python program for above approach
 
# A simple recursive approach
# to replace all
# pi in a given function with "3.14"
# Firstly function is declared we don't
# need any helper function one
# function is enough
 
 
def replacePi(string):
 
    # Base case if string is empty
    # or length of string is 1
    # return the string
    if len(string) == 0 or
                     len(string) == 1:
        return string
     
    # If the 0th and 1st element
    # of string are p
    # and i we have to handle them
    # for rest we have to call
    # recursion it will give the result
    if string[0] == 'p' and string[1] == 'i':
       
        # Smalloutput is a variable
        # used to store recursion result
        smallOutput = replacePi(string[2:])   
         
        # And we have to add the recursion
        # result with the first part we
          # handeled and return the answer
        return "3.14" + smallOutput            
    else:
         
        # If not then we have to call
        # recursion from 1st to all elements
        # then add recursion result to
        # 1st element and return it
        smallOutput = replacePi(string[1:])
        return string[0] + smallOutput
       
# Driver code
if __name__ == "__main__":
 
  string = "pipppiiipi"
 
  # Function call
  result = replacePi(string)
  print result

C#




// C# program for above approach
using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
 
class GFG {
 
    // A simple recursive approach
    // to replace all pi in a given
    // function with "3.14". Firstly
    // function is declared we don't
    // need any helper function one
    // function is enough
    static string replacePi(string s)
    {
 
        // Base case if s is empty
        // or length of s is 1
        // return the s
        if (s.Length == 0 || s.Length == 1)
            return s;
 
        // If the 0th and 1st element
        // of s are p and i we have to
        // handle them for rest we have
        // to call recursion it will
        // give the result
        if (s[0] == 'p' && s[1] == 'i') {
 
            // Smalloutput is a variable
            // used to store recursion result
            string smallOutput = replacePi(s.Substring(2));
 
            // And we have to add the recursion
            // result with the first part we
            // handeled and return the answer
            return "3.14" + smallOutput;
        }
        else {
 
            // If not then we have to call
            // recursion from 1st to all elements
            // then add recursion result to
            // 1st element and return it
            string smallOutput = replacePi(s.Substring(1));
            return s[0] + smallOutput;
        }
    }
 
    // Driver Code
    public static void Main(string[] args)
    {
        string s = "pipppiiipi";
 
        // Function call
        string result = replacePi(s);
        Console.Write(result);
    }
}
 
// This code is contributed by rutvik_56

Output:

3.14pp3.14ii3.14

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