Java Program to Print Downward Left Triangle Number Pattern - 3

In this program we print a downward left triangle number pattern. The first row prints the numbers 1 to 5, and each row after it starts one number later and one space further to the right, until only 5 is left.

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:

12345
 2345
  345
   45
    5

2. How the Program Works

Row number row needs two things: row - 1 spaces to push the numbers to the right, then the numbers from row up to the number of rows.

• The outer loop runs once for each row, from 1 to numberOfRows.
• The first inner loop prints row - 1 spaces.
• The second inner loop prints the numbers from row to numberOfRows.
• System.out.println() moves to the next line after each row.

3. Java Program

public class Pattern12 {
    public static void main(String[] args) {
        int numberOfRows = 5;

        // outer loop for the rows
        for (int row = 1; row <= numberOfRows; row++) {
            // inner loop to print the spaces
            for (int column = 1; column < row; column++) {
                System.out.print(" ");
            }
            // inner loop to print the numbers
            for (int column = row; column <= numberOfRows; column++) {
                System.out.print(column);
            }
            // move to the next line
            System.out.println();
        }
    }
}

12345
 2345
  345
   45
    5

4. Print the Pattern for Any Number of Rows

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

import java.util.Scanner;

public class Pattern12Input {
    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();

        for (int row = 1; row <= numberOfRows; row++) {
            for (int column = 1; column < row; column++) {
                System.out.print(" ");
            }
            for (int column = row; column <= numberOfRows; column++) {
                System.out.print(column);
            }
            System.out.println();
        }
    }
}

Enter the number of rows: 7
1234567
 234567
  34567
   4567
    567
     67
      7

5. Summary

• The outer loop picks the row; the inner loops print the spaces and the numbers for that row.
• Row row has row - 1 spaces and the numbers from row to numberOfRows.
• Each row is one number shorter than the one above it, which gives the downward triangle.

Related Programs

• Java Program to Print Downward Left Triangle Number Pattern - 1
• Java Program to Print Downward Left Triangle Number Pattern - 2
• Java Program to Print Downward Right Triangle Number Pattern - 3
• Java Program to Print Pyramid Number Pattern
• All Java Pattern Programs