JavaScript Program for Hollow Pyramid Star Pattern

In this article, we will demonstrate how to create Hollow Pyramid Star Patterns in JavaScript.

Possible Hollow Pyramid Star Patterns are

• Upper pyramid
• Inverted pyramid
• Left inverted pyramid
• Right inverted pyramid

Approach

There will be two different approaches based on alignments i.e. horizontal and vertical:

• Horizontally Inverted Pyramid
• Vertically Inverted Pyramid

Horizontally Inverted Pyramid

• This type includes the upper pyramid and the inverted pyramid.
• To achieve this we will use Nested For loops.
• The first loop will iterate N times for row iteration and initiate a new row string.
• Second loop will perform Double iteration and will contain the condition to print the required star pattern i.e.,
  • row + column == N +1
  • row+ N == coulmn + 1
  • row = = N

Example 1: Upper pyramid

Javascript

let n = 5;
for (let i = 1; i <= n; i++) {
    let str = ''
    for(let j = 1; j <= 2*n-1 ; ++j){
        if(i+j == n +1||(i+n==j+1) ||i==n)
        str+='* ';
        else
        str+='  ';
    }
    console.log(str);
}

Output

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

Example 2: Inverted pyramid

Javascript

let n = 5;
for (let i = n; i >= 1; i--) {
   let str = ''
    for(let j = 1; j <= 2*n-1 ; ++j){
        if(i+j == n +1||(i+n==j+1) ||i==n)
        str+='* ';
        else
        str+='  ';
    }
    console.log(str);
}

Output

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

Vertically Inverted Pyramid

• Vertically inverted pyramids include the Right inverted and Left inverted pyramids
• To achieve this we will use 2 Nested For loops to cover two halves of the pyramid i.e. right angle triangle and inverted right angle triangle and execute from 1 to N and back to 1.
• First or outer loop will iterate N times for iterating rows and initiate new string.
• Inner loop will also iterate and time and contain the right angle triangle .i.e.,
  • row + column == N+1
  • column == N
• After completion of both the loops we will get the complete vertically inverted hollow pattern.

Example1: Right inverted pyramid

Javascript

let n = 5;
for (let i = 1; i <= n; i++) {
    let str = ''
    for(let j = 1; j <= n ; ++j){
        if(i==j||j==1)
        str+='* ';
        else
        str+='  ';
    }

    console.log(str);
}
for (let i = n-1; i >= 1; i--) {
  let str = ''
    for(let j = 1; j <= n ; ++j){
        if(i==j||j==1)
        str+='* ';
        else
        str+='  ';
    }
    console.log(str);
}

Output

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

Example 2: Left inverted pyramid

Javascript

let n = 5;
for (let i = 1; i <= n; i++) {
    let str = ''
    for(let j = 1; j <= n ; ++j){
        if(i+j==1+n||j==n)
        str+='* ';
        else
        str+='  ';
    }

    console.log(str);
}
for (let i = n-1; i >= 1; i--) {
  let str = ''
    for(let j = 1; j <= n ; ++j){
        if(i+j==n+1||j==n)
        str+='* ';
        else
        str+='  ';
    }
    console.log(str);
}

Output

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