C++ Program To Print Inverted Hollow Star Pyramid Pattern

An inverted hollow star pyramid is a pattern where the first row contains stars across the entire width, while the following rows contain stars only at the boundaries. The remaining positions are filled with spaces, creating a hollow structure that narrows toward the bottom.

• The number of leading spaces increases by one after every row.
• The number of positions decreases by two in each successive row.

Illustration

Input:

R = 5

Output:

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

For R = 10, the pattern becomes:

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

Approach

The pattern can be generated using nested loops:

1. Print the required leading spaces for each row.
2. Calculate the number of positions in the current row.
3. Print * for the first row.
4. For the remaining rows, print * only at the first and last positions.
5. Print spaces between the boundary stars.
6. Move to the next row.

For row i, the number of positions containing stars or spaces is:

2 * R - (2 * i - 1)

This value decreases by two after every row.

#include <bits/stdc++.h>
using namespace std;

void print_patt(int R)
{
  // To iterate through the rows
  for(int i = 1; i <= R; i++)
  {
    // To print the  beginning spaces 
    for(int sp = 1; 
            sp <= i - 1 ; sp++)
    {
      cout << " ";
    }
      
    // Iterating from ith column to
    // last column (R*2 - (2*i - 1))
    int last_col = (R * 2 - (2 * i - 1));
        
    // To iterate through column
    for(int j = 1; j <= last_col; j++)
    {
      // To Print all star for first 
      // row (i==1) ith column (j==1) 
      // and for last column 
      // (R*2 - (2*i - 1))
      if(i == 1)
        cout << "*";
      else if(j == 1)
        cout << "*";
      else if(j == last_col)
        cout << "*";
      else
        cout << " ";
    }
        
    // After printing a row proceed 
    // to the next row
    cout << "\n";
  }
}

// Driver code
int main()
{
  // Number of rows
  int R = 5; 
  print_patt(R);
  return 0;
}

Output:

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