Chapter 5 Exercise 17, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

**5.17 (Display pyramid) Write a program that prompts the user to enter an integer from 1 to 15 and displays a pyramid, as shown in the following sample run:
    Enter the number of lines: 7
                1
              2 1 2
            3 2 1 2 3
          4 3 2 1 2 3 4
        5 4 3 2 1 2 3 4 5
      6 5 4 3 2 1 2 3 4 5 6
    7 6 5 4 3 2 1 2 3 4 5 6 7

Using four loops, one to loop through the line, one to print spaces and two other to print numbers, decreamentally and inecrementally.

                                             |line number|number of  2-spaces|
                1                                       1      |   (7-1)
              2 1 2                                   2      |   (7-2)
            3 2 1 2 3                               3      |   (7-3)
          4 3 2 1 2 3 4                           4      |   (7-4)
        5 4 3 2 1 2 3 4 5                       5      |   (7-5)
      6 5 4 3 2 1 2 3 4 5 6                   6      |   (7-6)
    7 6 5 4 3 2 1 2 3 4 5 6 7               7      |   (7-7)
                                                         8      |   (n-i)

import java.util.Scanner;
 
 
public class ProgrammingEx5_17 {
 
 public static void main(String[] args) {
 
  System.out.print("Enter the number of lines:");
  Scanner input = new Scanner(System.in);
   
  //get the total number of lines n.
  int n = input.nextInt();
   
  //Loop through the lines from 1 to n
  for (int i = 1; i <= n; i++) {
   // printing spaces, 2 at a time from j=1 to j= n-i 
   for (int j = 1; j <= (n - i); j++) {
    System.out.print("  ");
   }
    
   //Printing number decreamentally from the line number j to 1
   for (int j = i; j >= 1; j--) {
    System.out.print(j + " ");
   }
    
   //Printing number increamentally from 2 to line number j
   for (int j = 2; j <= i; j++) {
    System.out.print(j + " ");
   }
   System.out.println();
 
  }
 
 }
 
}