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Java Program to Print Downward Left Triangle Number Pattern - 2

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In this program we print a downward left triangle number pattern where each row repeats one number. The first row prints 5 five times, the next prints 4 four times, and so on down to a single 1.

Like every pattern program, it is built from nested loops: the outer loop picks the row, and the inner loops print what goes on that row.

1. The Pattern

For 5 rows the program prints:

Pattern
55555
 4444
  333
   22
    1

2. How the Program Works

Here is what each printed line is made of when numberOfRows is 5:

LineLeading spacesPrinted after the spaces
1055555
214444
32333
4322
541
  • The outer loop runs once for each row, from 1 to numberOfRows.
  • value is numberOfRows - row + 1: the number to print and also how many times to print it.
  • The first inner loop prints row - 1 spaces.
  • The second inner loop prints value, value times.
  • System.out.println() moves to the next line after each row.

3. Java Program

Pattern11.java 
public class Pattern11 {
    public static void main(String[] args) {
        int numberOfRows = 5;

        // outer loop for the rows
        for (int row = 1; row <= numberOfRows; row++) {
            int value = numberOfRows - row + 1;
            // inner loop to print the spaces
            for (int column = 1; column < row; column++) {
                System.out.print(" ");
            }
            // inner loop to print value, value times
            for (int column = 1; column <= value; column++) {
                System.out.print(value);
            }
            // move to the next line
            System.out.println();
        }
    }
}
Output
55555
 4444
  333
   22
    1

4. Print the Pattern for Any Number of Rows

To let the user choose the size of the pattern, read the number of rows with a Scanner. The loops stay the same.

Pattern11Input.java 
import java.util.Scanner;

public class Pattern11Input {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter the number of rows: ");
        int numberOfRows = scanner.nextInt();
        scanner.close();

        // outer loop for the rows
        for (int row = 1; row <= numberOfRows; row++) {
            int value = numberOfRows - row + 1;
            // inner loop to print the spaces
            for (int column = 1; column < row; column++) {
                System.out.print(" ");
            }
            // inner loop to print value, value times
            for (int column = 1; column <= value; column++) {
                System.out.print(value);
            }
            // move to the next line
            System.out.println();
        }
    }
}
Output (with sample input)
Enter the number of rows: 6
666666
 55555
  4444
   333
    22
     1
Note: once the pattern needs numbers above 9, two-digit numbers take up two positions and the shape is no longer lined up. Print each number with a fixed width, for example System.out.printf("%3d", value), and print three spaces wherever the program prints one, to keep it lined up.

5. Summary

  • The outer loop picks the row; the inner loops print the spaces and the numbers for that row.
  • Work out how many spaces and which numbers each row needs, then write one inner loop for each.
  • Keep numberOfRows in a variable, so the same program can print the pattern in any size.

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