Replace all occurrences of pi with 3.14 in a given string

Given a string, the task is to replace all occurrences of pi with 3.14 in the given string.

Examples: 

Input : str = "2 * pi + 3 * pi = 5 * pi"
Output : 2 * 3.14 + 3 * 3.14 = 5 * 3.14

Input : str = "pippppiiiipi"
Output : 3.14ppp3.14iii3.14

Input : str = "xpix"
Output : x3.14x

Approach 1:

1. Create an empty output string.
2. Traverse the string from the 0th index till second last index since length of pi is 2. 
3. If the alphabets at the current and (current+1)^th index form the word “pi”, append “3.14” to the output string. 
4. Else append the alphabet at the current index. 

Below is the implementation of the above approach: 

C++

// C++ program to replace all
// pi in a given string with 3.14

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

// Function to replace all occurrences
// of pi in a given with 3.14
string replacePi(string input)
{
    string output;

    int size = input.length();

    // Iterate through second last
    // element of the string
    for (int i = 0; i < size; ++i) {

        // If current and current +1 alphabets
        // form the word 'pi'
        // append 3.14 to output
        if (i + 1 < size and input[i] == 'p' and input[i + 1] == 'i') {
            output += "3.14";
            i++;
        }

        // Append the current letter
        else {
            output += input[i];
        }
    }

    // Return the output string
    return output;
}

// Driver Code
int main()
{
    string input = "2 * pi + 3 * pi = 5 * pi";
    cout << replacePi(input);
    return 0;
}

Java

// Java program to replace all
// pi in a given String with 3.14

class GFG {

    // Function to replace all occurrences
    // of pi in a given with 3.14
    public String replacePi(String input)
    {
        String output = "";

        int size = input.length();

        // Iterate through second last
        // element of the String
        for (int i = 0; i < size; ++i) {
            // If current and current +1 alphabets
            // form the word 'pi'
            // append 3.14 to output
            if (i + 1 < size && input.charAt(i) == 'p' && input.charAt(i + 1) == 'i') {
                output += "3.14";
                i++;
            }

            // Append the current letter
            else {
                output += input.charAt(i);
            }
        }

        // Return the output String
        return output;
    }

    // Driver Code
    public static void main(String args[])
    {
        GFG g = new GFG();
        String input = "2 * pi + 3 * pi = 5 * pi";
        System.out.println(g.replacePi(input));
    }
}

// This code has been contributed by 29AjayKumar

Python3

# Python program to replace all
# pi in a given string with 3.14

# Function to replace all occurrences
# of pi in a given with 3.14
def replacePi(input):
    output ="";

    size = len(input);

    # Iterate through second last
    # element of the string
    for i in range(size):

        # If current and current + 1 alphabets
        # form the word 'pi'
        # append 3.14 to output
        if (i + 1 < size and input[i] == 'p' and
                            input[i + 1] == 'i'):
            output += "3.14";
            i+= 1;

        # Append the current letter
        else:
            output += input[i];
    # Return the output string
    return output;

# Driver Code
input = "2 * pi + 3 * pi = 5 * pi";
print(replacePi(input));

# This code contributed by PrinciRaj1992

C#

// C# program to replace all
// pi in a given string with 3.14

using System;
// Function to replace all occurrences
// of pi in a given with 3.14
class gfg {
    public string replacePi(string input)
    {
        string output = "";

        int size = input.Length;

        // Iterate through second last
        // element of the string
        for (int i = 0; i < size; ++i) {
            // If current and current +1 alphabets
            // form the word 'pi'
            // append 3.14 to output
            if (i + 1 < size && input[i] == 'p' && input[i + 1] == 'i') {
                output += "3.14";
                i++;
            }

            // Append the current letter
            else {
                output += input[i];
            }
        }

        // Return the output string
        return output;
    }
}

// Driver Code
class geek {
    public static int Main()
    {
        gfg g = new gfg();
        string input = "2 * pi + 3 * pi = 5 * pi";
        Console.WriteLine(g.replacePi(input));
        return 0;
    }
}
// This code is contributed by Soumik

Javascript

<script>

      // JavaScript program to replace all
      // pi in a given string with 3.14

      // Function to replace all occurrences
      // of pi in a given with 3.14
      function replacePi(input) {
        var output = "";

        var size = input.length;

        // Iterate through second last
        // element of the string
        for (var i = 0; i < size; ++i) {
          // If current and current +1 alphabets
          // form the word 'pi'
          // append 3.14 to output
          if (i + 1 < size && input[i] === "p"
          && input[i + 1] === "i")
          {
            output += "3.14";
            i++;
          }

          // Append the current letter
          else {
            output += input[i];
          }
        }

        // Return the output string
        return output;
      }

      // Driver Code
      var input = "2 * pi + 3 * pi = 5 * pi";
      document.write(replacePi(input));

</script>

Output

2 * 3.14 + 3 * 3.14 = 5 * 3.14

Time Complexity: O(N), where N is the length of the given string.
Auxiliary Space: O(1) 

Approach 2: (In Java)

To replace all the PI occurrences to 3.14, use replaceAll() method of Java String Class.

C++

#include <iostream>
#include <string>

using namespace std;

int main()
{

    // Declare a string
    string expression = "2 * pi + 3 * pi = 5 * pi";

    // Call replace() method to replace PI to 3.14
    size_t pos = expression.find("pi");
    while (pos != string::npos)
    {
        expression.replace(pos, 2, "3.14");
        pos = expression.find("pi", pos + 1);
    }

    // Print the result
    cout << expression << endl;

    return 0;
}

Java

public class ReplacePI {
    public static void main(String[] args)
    {
        // Declare a String
        String expression = "2 * pi + 3 * pi = 5 * pi";

        // Call replaceAll() method to replace PI to 3.14
        expression = expression.replaceAll("pi", "3.14");

        // Print the result
        System.out.println(expression);
    }
}

Python3

# Declare a string
expression = "2 * pi + 3 * pi = 5 * pi"

# Call replace() method to replace PI to 3.14
expression = expression.replace("pi", "3.14")

# Print the result
print(expression)

# This code is contributed by codebraxnzt

C#

using System;

class Program {
    static void Main() {
        // Declare a string
        string expression = "2 * pi + 3 * pi = 5 * pi";

        // Call replace() method to replace PI to 3.14
        int pos = expression.IndexOf("pi");
        while (pos != -1) {
            expression = expression.Substring(0, pos) + "3.14" + expression.Substring(pos + 2);
            pos = expression.IndexOf("pi", pos + 1);
        }

        // Print the result
        Console.WriteLine(expression);
    }
}

Javascript

// JavaScript equivalent code

// Declare a string
let expression = "2 * pi + 3 * pi = 5 * pi";

// Call replace() method to replace PI to 3.14
let pos = expression.indexOf("pi");
while (pos !== -1)
{
    expression = expression.slice(0, pos) + "3.14" + expression.slice(pos + 2);
    pos = expression.indexOf("pi", pos + 1);
}

// Print the result
console.log(expression);

Output

2 * 3.14 + 3 * 3.14 = 5 * 3.14

Time Complexity: O(N), where N is the length of the given string.
Auxiliary Space: O(N)