Java Program:

Example:

1
1 2
1 2 3
1 2
1

import java.util.Scanner;

public class Pattern {

  public static void main(String[] args) {
    Scanner userInput = new Scanner(System.in);
    System.out.print("Enter number of columns : ");

    int columns,trows,k,num;
    columns=userInput.nextInt();
    trows=2*columns-1;
    k=1;
    for(int i=1; i<=trows; i++) {
      num=1;
      for(int j=1; j<=k; j++) {
        System.out.print(num++ +" ");
      }
      if(i<columns)k++;
      else k--;
      System.out.print("\n");
    }

  }
}

Output:

Enter number of columns: 4

1
1 2
1 2 3
1 2 3 4
1 2 3
1 2
1

Main Logic :

trows=2*columns-1;   // trows : total rows to print
k=1;  // Used to trigger decreasing order of number

for(int i=1; i<=trows; i++) {
  num=1;
  for(int j=1; j<=k; j++) {
    System.out.print(num++ +" ");
  }
  //check for position change at which triangle number value to decrease
  if(i<columns)k++;
  else k--;

  System.out.print("\n");
}