Java: Form a staircase shape of n coins where every k-th row must have exactly k coins

Last update on April 01 2025 10:50:25 (UTC/GMT +8 hours)

Staircase Coins

Write a Java program to form a staircase shape of n coins where every k-th row must have exactly k coins.

Example 1:
n = 3
The coins can form the following rows:
$
$ $
We will return 2 rows.
Example 2:
n = 4
The coins can form the following rows:
$
$ $
$
We will return 2 rows as the 3rd row is incomplete.
Example 3:
n = 5
The coins can form the following rows:
$
$ $
$ $
We will return 2 rows as the 3rd row is incomplete.

Sample Solution:

Java Code:

import java.util.Scanner;

public class Example109 {
    public static void main(String[] arg) {
        // Create a Scanner object for user input
        Scanner in = new Scanner(System.in);

        // Prompt the user to input a positive integer
        System.out.print("Input a positive integer: ");
        
        // Read the user's input as an integer
        int n = in.nextInt(); 

        if (n > 0) {
            // Check if n is a positive integer
            double sqrtResult = Math.sqrt(8 * (long) n + 1);  // Calculate the square root
            int numRows = (int) ((sqrtResult - 1) / 2);      // Calculate the number of rows
            System.out.println("Number of rows: " + numRows);
        }
        
        // Close the input scanner
        in.close();
    }	
}

Sample Output:

Input a positive integer: 5                                            
Number of rows: 2 

Flowchart:

For more Practice: Solve these Related Problems:

• Modify the program to return the number of complete rows that can be formed.
• Write a program to find how many more coins are needed to complete the next row.
• Modify the program to print the staircase structure visually.
• Write a program to return the sum of coins in the completed rows.

Java Code Editor:

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