Print Butterfly Pattern

Given a number n, print Butterfly pattern using '*' character. The pattern contains 2n - 1 rows, with the upper half expanding from 1 to n stars on each side and the lower half contracting from n - 1 to 1 star on each side, with spaces separating the two halves.

Examples:

Input: n = 4
Output:
* *
** **
*** ***
*******
*** ***
** **
* *
Explanation: The pattern contains 7 rows, expanding from 1 to 4 stars on each side and then contracting symmetrically.

Input: n = 5
Output:
* *
** **
*** ***
**** ****
*********
**** ****
*** ***
** **
* *
Explanation: The pattern contains 9 rows, expanding from 1 to 5 stars on each side and then contracting symmetrically.

Nested Loops with Incremental and Decremental Stars - O(n ^ 2) Time and O(1) Space

The idea is to print the butterfly pattern using 2n - 1 rows.

• Maintain the number of stars on each side and the spaces between them.
• In the upper half, increase the stars by one and decrease the spaces by two in each row.
• In the lower half, decrease the stars by one and increase the spaces by two to create a symmetric butterfly pattern.

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

void printButterflyPattern(int n)
{
    int spaces = 2 * n - 1;
    int stars = 0;

    // Iterate through all 2*n - 1 rows.
    for (int i = 1; i <= 2 * n - 1; i++)
    {
        // Update stars and spaces for the current row.
        if (i <= n)
        {
            stars++;
            spaces -= 2;
        }
        else
        {
            stars--;
            spaces += 2;
        }

        // Print stars on the left side.
        for (int j = 1; j <= stars; j++)
        {
            cout << "*";
        }

        // Print spaces between the two halves.
        for (int j = 1; j <= spaces; j++)
        {
            cout << " ";
        }

        // Print stars on the right side.
        for (int j = 1; j <= stars; j++)
        {
            if (j != n)
            {
                cout << "*";
            }
        }

        // Move to the next line.
        cout << endl;
    }
}

int main()
{
    int n = 4;
    printButterflyPattern(n);

    return 0;
}

class GFG {
    static void printButterflyPattern(int n)
    {
        int spaces = 2 * n - 1;
        int stars = 0;

        // Iterate through all 2*n - 1 rows.
        for (int i = 1; i <= 2 * n - 1; i++) {

            // Update stars and spaces for the current row.
            if (i <= n) {
                stars++;
                spaces -= 2;
            }
            else {
                stars--;
                spaces += 2;
            }

            // Print stars on the left side.
            for (int j = 1; j <= stars; j++) {
                System.out.print("*");
            }

            // Print spaces between the two halves.
            for (int j = 1; j <= spaces; j++) {
                System.out.print(" ");
            }

            // Print stars on the right side.
            for (int j = 1; j <= stars; j++) {
                if (j != n) {
                    System.out.print("*");
                }
            }

            // Move to the next line.
            System.out.println();
        }
    }

    public static void main(String[] args)
    {
        int n = 4;
        printButterflyPattern(n);
    }
}

def printButterflyPattern(n):
    spaces = 2 * n - 1
    stars = 0

    # Iterate through all 2*n - 1 rows.
    for i in range(1, 2 * n):

        # Update stars and spaces for the current row.
        if i <= n:
            stars += 1
            spaces -= 2
        else:
            stars -= 1
            spaces += 2

        # Print stars on the left side.
        for j in range(1, stars + 1):
            print("*", end="")

        # Print spaces between the two halves.
        for j in range(1, spaces + 1):
            print(" ", end="")

        # Print stars on the right side.
        for j in range(1, stars + 1):
            if j != n:
                print("*", end="")

        # Move to the next line.
        print()


# Driver Code
if __name__ == "__main__":
    n = 4
    printButterflyPattern(n)

using System;

class GFG {
    static void printButterflyPattern(int n)
    {
        int spaces = 2 * n - 1;
        int stars = 0;

        // Iterate through all 2*n - 1 rows.
        for (int i = 1; i <= 2 * n - 1; i++) {

            // Update stars and spaces for the current row.
            if (i <= n) {
                stars++;
                spaces -= 2;
            }
            else {
                stars--;
                spaces += 2;
            }

            // Print stars on the left side.
            for (int j = 1; j <= stars; j++) {
                Console.Write("*");
            }

            // Print spaces between the two halves.
            for (int j = 1; j <= spaces; j++) {
                Console.Write(" ");
            }

            // Print stars on the right side.
            for (int j = 1; j <= stars; j++) {
                if (j != n) {
                    Console.Write("*");
                }
            }

            // Move to the next line.
            Console.WriteLine();
        }
    }

    static void Main()
    {
        int n = 4;
        printButterflyPattern(n);
    }
}

function printButterflyPattern(n)
{
    let spaces = 2 * n - 1;
    let stars = 0;

    // Iterate through all 2*n - 1 rows.
    for (let i = 1; i <= 2 * n - 1; i++) {

        // Update stars and spaces for the current row.
        if (i <= n) {
            stars++;
            spaces -= 2;
        }
        else {
            stars--;
            spaces += 2;
        }

        // Print stars on the left side.
        for (let j = 1; j <= stars; j++) {
            process.stdout.write("*");
        }

        // Print spaces between the two halves.
        for (let j = 1; j <= spaces; j++) {
            process.stdout.write(" ");
        }

        // Print stars on the right side.
        for (let j = 1; j <= stars; j++) {
            if (j !== n) {
                process.stdout.write("*");
            }
        }

        // Move to the next line.
        console.log();
    }
}


// Driver Code
const n = 4;
printButterflyPattern(n);

Output: