Hollow Diamond Pattern

Given an integer N, print the pattern shown below.

Examples:

Input: N=5
Output:

Input: N=3
Output:

Using Nested Loops - O(n^2) Time and O(1) Space

Iterate through 2 × n − 1 rows to form the upper and lower parts of the pattern, and compute a variable (comp) to control the spacing for each row.
Print leading spaces using an inner loop so that the stars shift toward the center and form the desired shape.
Use another inner loop to print stars at the first and last positions of the row and spaces in between, creating a hollow pattern.

C++

#include <iostream>
using namespace std;

int main() {
    int n = 3;

    // Outer loop for rows
    for (int i = 0; i < 2 * n - 1; i++) {

        int comp;
        if (i < n)
            comp = 2 * (n - i) - 1;
        else
            comp = 2 * (i - n + 1) + 1;

        // Print leading spaces
        for (int j = 0; j < comp; j++)
            cout << " ";

        // Print stars and inner spaces
        for (int k = 0; k < 2 * n - comp; k++) {
            if (k == 0 || k == 2 * n - comp - 1)
                cout << "* ";
            else
                cout << "  ";
        }

        cout << endl;
    }

    return 0;
}

Java

public class Gfg{
    public static void main(String[] args) {
        int n = 3;

        // Outer loop for rows
        for (int i = 0; i < 2 * n - 1; i++) {

            int comp;
            if (i < n)
                comp = 2 * (n - i) - 1;
            else
                comp = 2 * (i - n + 1) + 1;

            // Print leading spaces
            for (int j = 0; j < comp; j++)
                System.out.print(" ");

            // Print stars and inner spaces
            for (int k = 0; k < 2 * n - comp; k++) {
                if (k == 0 || k == 2 * n - comp - 1)
                    System.out.print("* ");
                else
                    System.out.print("  ");
            }

            System.out.println();
        }
    }
}

Python

def main():
    n = 3

    # Outer loop for rows
    for i in range(2 * n - 1):

        comp = 2 * (n - i) - 1 if i < n else 2 * (i - n + 1) + 1

        # Print leading spaces
        for j in range(comp):
            print(' ', end='')

        # Print stars and inner spaces
        for k in range(2 * n - comp):
            if k == 0 or k == 2 * n - comp - 1:
                print('* ', end='')
            else:
                print('  ', end='')

        print()


if __name__ == "__main__":
    main()

using System;

public class GfG
{
    public static void Main()
    {
        int n = 3;

        // Outer loop for rows
        for (int i = 0; i < 2 * n - 1; i++)
        {
            int comp = i < n ? 2 * (n - i) - 1 : 2 * (i - n + 1) + 1;

            // Print leading spaces
            for (int j = 0; j < comp; j++)
                Console.Write(" ");

            // Print stars and inner spaces
            for (int k = 0; k < 2 * n - comp; k++)
            {
                if (k == 0 || k == 2 * n - comp - 1)
                    Console.Write("* ");
                else
                    Console.Write("  ");
            }

            Console.WriteLine();
        }
    }
}

JavaScript

function printPattern(n) {

    // Outer loop for rows
    for (let i = 0; i < 2 * n - 1; i++) {

        let comp = i < n ? 2 * (n - i) - 1 : 2 * (i - n + 1) + 1;

        // Print leading spaces
        let spaces = ' '.repeat(comp);

        let stars;
        if (2 * n - comp === 1) {
            stars = '*';  // single star case
        } else {
            stars = '*' + ' '.repeat((2 * n - comp - 2) * 2) + '*';
        }

        console.log(spaces + stars);
    }
}

// Function call
printPattern(3);

Output

Using Nested Loops - O(n^2) Time and O(1) Space

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