How to print a pyramid pattern using JavaScript

In this answer, we will learn to solve a common coding problem pattern. We will print a star pyramid pattern using JavaScript.

Desired output

We will print the below pattern:

Now let’s explore two different approaches to achieve this result.

Naive approach

We will use the following three for loops:

  • One is the outer loop for rows of the pyramid.

  • The other two are nested loops, where the first inner loop will print the number of spaces (' ') and the second will print the number of stars (*).

Code

Let’s see the program to create a pyramid pattern:

let n = 5;
// External loop
for (let i = 1; i <= n; i++) {
  // printing spaces
  for (let j = 1; j <= n - i; j++) {
    process.stdout.write(' ')
  }
  // printing stars
  for (let k = 0; k < 2 * i - 1; k++) {
    process.stdout.write('*')
  }
  console.log();
}

Explanation

  • Line 1: We initialize a variable n with an integer representing the total number of rows that make up the pyramid. We can also consider this as the height of the pyramid.

  • Line 3: We have the first for loop that will iterate over the total number of rows (5, in the example above).

  • Lines 5 to 7: We have the first nested for loop to print spaces n-i times, where i is the current iteration of the outer loop. For example, if i= 3, we will print 2 spaces in the third row using process.stdout.write(' ').

  • Lines 9 to 11: We have the second nested for loop to print stars 2 * i - 1 times, where i is the current iteration of outer loop. For example, if i= 3, we will print 5 stars in the third row using process.stdout.write('*').

  • Line 12: We used console.log() with null, as it will change to a new line. We can also use process.stdout.write('\n') to change the line.

Optimise approach

We will use only a single for loop to achieve the desired results:

  • Use one loop to iterate through each row.

  • Determine the number of spaces and asterisks for each row using simple calculations.

  • Utilize string repetition to construct each row efficiently.

  • Reduce nested loops for better performance and readability.

Code

Let's see the program to create a pyramid pattern:

function printPyramid(rows) {
    let pyramid = '';
    // Defined a for loop to iteracte through each row
    for (let i = 0; i < rows; i++) {
        // Add spaces before the first '*' to center the pyramid
        pyramid += ' '.repeat(rows - i - 1);
        // Add '*' for the current row
        pyramid += '*'.repeat(2 * i + 1);
        // Move to the next line
        pyramid += '\n';
    }
    console.log(pyramid);
}
// Example usage: Print a pyramid with 5 rows
printPyramid(5);

Explanation

  • Line 4: We Defined a for loop to iterate through each row.

  • Line 6: We calculated to add spaces before the first * to center the pyramid.

  • Line 8: We added * for that specific role where our for loop is iterating through.

  • Line 10: We brake the line to move over to next line.

Conclusion

We completed the task to print *'s in a form that looks like a pyramid. However, this answer shows both a naive and optimise approach to do it. However, there can be several algorithms to achieve the same result.

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