Pyramid Star Pattern

Pattern consists of N (for this case 5) rows. Each row contains 2*i-1(where i is the current row number) stars. In addition to stars, the pattern has leading spaces. Each row contains some spaces. To count total spaces per row point your mouse over the above pattern. How many leading spaces are there in each row?? Try to figure that out as we will need to print that number of spaces first then stars.

For N=5 as given the output pattern

Row 1: 4 spaces // N-current row number=?(5-1=4)

Row 2: 3 spaces // N-current row number=?(5-2=3)

Row 3: 2 spaces // N-current row number=?(5-3=2)

Row 4: 1 spaces // N-current row number=?(5-4=1)

Row 5: 0 spaces // N-current row number=?(5-5=0)

N - current row number = Number of spaces in the current row

Now give it a try !!

1. Input number of rows to print from user. Store it in a variable say N.
2. To iterate through rows, run an outer loop from 1 to N. The loop structure should look like for(i=1; i<=N; i++).
3. To print spaces, run an inner loop from 1 to N-i. The loop structure should look like for(j=1; j<=N-i; j++). Inside this loop print single space.
4. To print star, run another inner loop from 1 to 2 * i - 1. The loop structure should look like for(j=1; j<=(2*i - 1); j++). Inside this loop print star.
5. After printing stars for current row, move to next line i.e. print new line.

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {

        // Input total number of rows from the user
        System.out.println("Enter number of rows: ");
        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt(); //total rows

        /* Iterate through rows */
        for (int i = 1; i <= N; i++) {
            /* Print leading spaces */
            for (int j = 1; j <= N - i; j++) {
                System.out.print(" ");
            }

            /* Print star */
            for (int j = 1; j <= (2 * i - 1); j++) {
                System.out.print("*");
            }

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

        scanner.close();
    }
}

If you notice carefully, you will find that the logic to print a hollow pyramid is almost similar to the pyramid star pattern(problem 1) logic. Just with this pattern you need to print stars only for the first column, last column, first row and last row.

If we relate to the first problem, in addition to stars, the pattern had leading spaces before the stars in each row. Each row contains some leading spaces. To count the total leading spaces per row point your mouse over the above pattern. How many leading spaces are there in each row?? There are N-i( i is the current row number) leading spaces. (We have already found this in Intuition of problem 1).

Iterate over N rows and first print leading spaces in every row. How will you print leading spaces? Hint: Use a for loop

After printing the leading spaces, now start with the logic to print hollow pyramid. At max, there can be (2*i-1) stars in row. We basically need to print two things "*"(asterisks) and " "(space) now. Think of conditions. When you will print what? Print star for the first column(j==1), first row(i==1), last column(j==2*i-1) or last row(i==N) otherwise print space. Do we need (i==1) compulsorily? No, We can remove that if we want because (j==1) would cater to that condition as well.

Now give it a try !!

1. Input number of rows to print from user. Store it in a variable say N.
2. To iterate through rows run an outer loop from 1 to N. The loop structure should look like for(i=1; i<=N; i++).
3. To print spaces, run an inner loop from 1 to N- i. The loop structure should look like for(j=1; j<=N-i; j++). Inside this loop print single space.
4. To print star, run another inner loop from 1 to 2*i-1. The loop structure should look like for (j=1; j<=(2*i-1); j++). Inside this loop print star for first column(j==1), first row(i==1), last column(j==2*i-1) or last row(i==N). Otherwise, print space.
5. After printing all columns of a row, move to next line i.e. print new line.

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {

        // Input total number of rows from the user
        System.out.println("Enter number of rows: ");
        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt(); //total rows

        for (int i = 1; i <= N; i++) {
            /* Print leading spaces */
            for (int j = 1; j <= N - i; j++) {
                System.out.print(" ");
            }

            /* Print hollow pyramid */
            for (int j = 1; j <= (2 * i - 1); j++) {
                /*
                 * Print star for last row (i==rows),
                 * first column(j==1) and for
                 * last column (j==(2*i-1)).
                 */
                if (i == 1 || i == N || j == 1 || j == (2 * i - 1)) {
                    System.out.print("*");
                } else {
                    System.out.print(" ");
                }
            }

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

        scanner.close();
    }
}

Pattern consists of N (for this case 5) rows.

To solve this question, we essentially need to find two things :

1)Relationship between current row number and leading spaces in that row

2)Relationship between current row number and number of stars in that row

Take out your pen and paper and try to find out the above two things.

The pattern consists of leading spaces. Each row contains i – 1 leading space (where i is the current row number).

Each row has exactly 2 * N - (2 * i - 1) stars.

Now give it a try !!

1. Input number of rows to print from user. Store it in a variable say N.
2. To iterate through rows, run an outer loop from 1 to N. The loop structure should look like for(i=1; i<=N; i++).
3. To print spaces, run an inner loop from 1 to i - 1 . The loop structure should look like for(j=1; j<i; j++). Inside this loop print single space.
4. To print stars, run another inner loop from 1 to 2 * N - (2 * i - 1). The loop structure should look like for(j=1; j<= (2*N - (2*i-1)); j++). Inside this loop print star.
5. After printing all stars for each row, move to next line i.e. print new line.

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {

        // Input total number of rows from the user
        System.out.println("Enter number of rows: ");
        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt(); //total rows

        for (int i = 1; i <= N; i++) {
            /* Print leading spaces */
            for (int j = 1; j < i; j++) {
                System.out.print(" ");
            }

            /* Print stars */
            for (int j = 1; j <= (2 * N - (2 * i - 1)); j++) {
                System.out.print("*");
            }

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

        scanner.close();
    }
}

The above pattern is similar to inverted pyramid star pattern with stars printed only for first or last column and for first or last row.(If you remember 🙂 we had a similar condition in problem 2 as well where stars were printed only for first or last column and for first or last row)

We will iterate through N rows. For each row, First, we will print the leading spaces and then we can use logic of hollow pyramid star pattern(problem 2). And then we will get our pattern. Make sense or not?? I hope yes ✌️.

Now please give it a try !! If you get the solution by just reading the intuition. Congratulations 🥳🫡. Otherwise, definitely, we can refer to the solution.

1. Input number of rows to print from user. Store it in a variable say N.
2. To iterate through rows, run an outer loop from 1 to N. The loop structure should look like for(i=1; i<=N; i++).
3. To print leading spaces, run an inner loop from 1 to i - 1. The loop structure should look like for(j=1; j<i; j++). Inside this loop print single space.
4. To print stars, run another inner loop from 1 to 2* N - (2 * i - 1). The loop structure should look like for(j=1; j<=(2*N-(2*i-1)); j++).Inside this loop print star for first column(j==1), first row(i==1), last column(j==2*i-1) or last row(i==N). Otherwise, print space.
5. After printing all columns of a row, move to next line i.e. print new line.

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {

        // Input number of rows from the user
        System.out.println("Enter number of rows: ");
        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt(); //total rows

        /* Iterate through rows */
        for (int i = 1; i <= N; i++) {
            /* Print leading spaces */
            for (int j = 1; j < i; j++) {
                System.out.print(" ");
            }

            /* Print hollow pyramid */
            for (int j = 1; j <= (2 * N - (2 * i - 1)); j++) {
                /*
                 * Print star for first row(i==1),
                 * last row(i==N)
                 * first column (j==1) and for
                 * last column (rows*2-(2*i-1))
                 */
                if (i == 1 || i == N || j == 1 || j == (2 * N - (2 * i - 1))) {
                    System.out.print("*");
                } else {
                    System.out.print(" ");
                }
            }

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

        scanner.close();
    }
}