How can I print to the console this table of numbers in Java?

Question

Asking for a natural number n, I want to print to the console in this format:

                1
              2 1
            3 2 1
          4 3 2 1
        5 4 3 2 1
          .
          .
          .
n . . . 5 4 3 2 1

Inputting 4, this is what I have so far:

    1
   21
  321
 4321

I want to add a space between the numbers. This is my code:

import java.util.Scanner;
public class PatternTwo {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int userInput;
        System.out.println("Please enter a number 1...9 : ");
        userInput = in.nextInt();
        String s="";
        int temp = userInput;
        for(int i=1; i<=userInput; i++ ) {

            for (int k= userInput; k>=i; k-- ) {
                System.out.printf(" ");
            }

            for(int j =i; j>=1; j-- ) {
                System.out.print(j);
            }


            System.out.println("");
        }

    }

}

Answer 1

Another alternative way could be to separate the spacing for each line using printf and using String.format for each number.

String.format("%1$" + length + "s", inputString) 

returns the inputString if inputString.length >= lengthelse the inputString padded with spaces so that the length equal to the given length.

Example:

public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    int userInput;
    System.out.println("Please enter a number 1...9 : ");// you can use this also for numbers > 9
    userInput = in.nextInt();
    int digits = String.valueOf(userInput).length()+1;
    for(int i = 1; i<=userInput; i++){
        System.out.printf("%1$"+(digits*(userInput-i+1))+"s","");
        for(int k = userInput - (userInput-i); k >= 1; k--){
            System.out.print(String.format("%1$"+digits+"s", k));
        }
        System.out.println();
    }
}

Answer 2

Below is a modification of your answer that does not print unnecessary extra white space when k equals i by modifying your k for-loops exit condition and similarly when j equals i by dealing with that case separately.

The main overall change is that in your k-loop you need to print 2 spaces rather than 1 to achieve your desired right side alignment:

import java.util.Scanner;

class PatternTwo {

  private static void printPatternTwo(int n) {
    for (int i = 1; i <= n; i++) {
      for (int k = n; k > i; k--) {
        System.out.print("  ");
      }
      for (int j = i; j >= 1; j--) {
        System.out.print(j == i ? j : " " + j);
      }
      System.out.println();
    }
  }

  public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);

    System.out.print("Please enter an integer between 1 and 9 inclusive: ");
    int userNum = -1;
    while (scanner.hasNext()) {
      if (scanner.hasNextInt()) {
        userNum = scanner.nextInt();
        if (userNum >= 1 && userNum <= 9) {
          scanner.close();
          break;
        } else {
          System.out.println("ERROR: Input number was not between 1 and 9");
          System.out.print("Enter a single digit number: ");
        }
      } else {
        System.out.println("ERROR: Invalid Input");
        System.out.print("Please enter an integer between 1 and 9 inclusive: ");
        scanner.next();
      }
    }

    printPatternTwo(userNum);
  }
}

Example Usage:

Please enter an integer between 1 and 9 inclusive: 12
ERROR: Input number was not between 1 and 9
Enter a single digit number: a
ERROR: Invalid Input
Please enter an integer between 1 and 9 inclusive: 5
        1
      2 1
    3 2 1
  4 3 2 1
5 4 3 2 1

Answer 3

Add a space in front of the number to be printed and double the spaces above so that it is not a pyramid. Something like this:

import java.util.Scanner;
public class PatternTwo {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int userInput;
        System.out.println("Please enter a number 1...9 : ");
        userInput = in.nextInt();
        String s="";
        int temp = userInput;
        for(int i=1; i<=userInput; i++ ) {

            for (int k= userInput; k>i; k-- ) { // <- corrected condition
                System.out.printf("  ");
            }

            for(int j = i; j>=1; j-- ) {
                System.out.print(j);

                // check if not 1 to avoid a trailing space
                if (j != 1) {
                    System.out.print(" ");
                }
            }


            System.out.println("");
        }

    }

}

EDIT

Thanks to /u/shash678 I corrected my solution to remove all unnecessary or wrong spaces

Answer 4

If you are comfortable with streams:

public class PatternTwo {

  public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    int userInput;
    System.out.println("Please enter a number 1...9 : ");
    userInput = in.nextInt();
    String s = "";
    int temp = userInput;

    revRange(1, temp).forEach(n -> printNumbers(n, temp));
  }

  static IntStream revRange(int from, int to) {
    return IntStream.range(from, to)
      .map(i -> to - i + from - 1);
  }

  private static void printNumbers(int n, int max) {
    IntStream.rangeClosed(0, n -1)
      .forEach(num -> System.out.print("  "));
    revRange(1, max - n)
      .forEach(num -> System.out.print(num + " "));
    System.out.println();
  }
}

Answer 5

How about a cleaner solution, which avoids using nested for-loops:

public static void main(final String[] args) {
    final Scanner scanner = new Scanner(System.in);
    System.out.print("Please enter a number 1...9 : ");
    final int n = scanner.nextInt();

    final ArrayList<String> suffixes = new ArrayList<>();
    for (int i = 1; i <= n; i++) {
        suffixes.add(0, i + " ");

        final String prefix = String.join("", Collections.nCopies(n - i, "  "));
        final String suffix = String.join("", suffixes);

        System.out.println(prefix + suffix);
    }
}

Answer 6

When printing the number put a space in from of it.

// this works up n == 9
System.out.print(" " + j); 

For n > 9 the issue is that you need to print the number and whitespaces on a fixed amount of space however the number of chars a number contains changes. A solution would be to use tab (or several if you want really big numbers).

// when printing blank spaces use a tab instead
for (int k= userInput; k>=i; k-- ) {
    System.out.printf("\t");
}

// then print number with tab in front
for(int j =i; j>=1; j-- ) {
    System.out.print("\t"+j);
}