JavaScript Program to Print Inverted Pyramid

In JavaScript, the Inverted Pyramid is the geometric pattern of “*” that is arranged in the format upside-down. This can be printed using various approaches like Looping, Recursion, and built-in methods.

Using Nested for Loop

This approach uses the for loop to print the inverted pyramid by using nested loops we control the spacing and the number of “*” in each row. The outer loop mainly manages the rows and the inner loop controls the leading spaces and printing “*” in the pattern.

Syntax:

for (initialization; condition; iteration) {
     for ((initialization; condition; iteration){
         //code
     }
    // code
}

Example: To demonstrate printing an Inverted Pyramid in JavaScript using the Nested for loop in JavaScript.

Javascript

let r = 5;
for (let i = r; i >= 1; i--) {
    for (let j = r - i; j > 0; j--) {
        process.stdout.write("  ");
    }
    for (let k = 0; k < 2 * i - 1; k++) {
        process.stdout.write("* ");
    }
    console.log();
}

Output

* * * * * * * * * 
  * * * * * * * 
    * * * * * 
      * * * 
        * 

Using Recursion

In the below approach, we have used the Recursive function which controls the row-wise printing by adjusting the leading spaces and the number of “*” in each row. The base cases make sure that the recursion ends when the “n” exceeds the total rows.

Syntax:

function recursiveFunction(parameters) {
    // Base case
    if (condition);
    // recursive
    return recursiveFunction(modifiedParameters);
}
// call
recursiveFunction(initialParameters);

Example: To demonstrate printing an Inverted Pyramind in JavaScript using recursion in JavaScript.

Javascript

function recursiveFn(n, tRows) {
    if (n <= tRows) {
        process.stdout.write("  ".repeat(n - 1));
        process.stdout.write("* ".repeat(2 * (tRows - n) + 1));
        console.log();
        recursiveFn(n + 1, tRows);
    }
}
let r = 5;
recursiveFn(1, r);

Output

* * * * * * * * * 
  * * * * * * * 
    * * * * * 
      * * * 
        * 

Using Array and Join methods

In this approach, we use the Array and Join method to iterate over each row, constructing the strings of leading spaces and the “*” pattern. The resulting string is then pushed into the array and last, the array is joined with the newline character, and the pattern is printed.

Syntax:

let newArray = Array(element1, element2, ..., elementN); 
let resultString = array.join(separator);

Example: To demonstrate printing an Inverted Pyramid in JavaScript using Array and the Join method in JavaScript.

Javascript

let r = 5;
let res = [];

for (let i = r; i >= 1; i--) {
    let s = Array(r - i + 1).join("  ");
    let stars = Array(2 * i - 1).fill("* ").join("");
    res.push(s + stars);
}
console.log(res.join('\n'));

Output

* * * * * * * * * 
  * * * * * * * 
    * * * * * 
      * * * 
        *