Kotlin Program:

Example:

1
1 2
1 2 3
1 2
1

fun main(args: Array<String>) {
  print("Enter number of columns : ") 
  val userInput = readLine()!!
  var columns:Int =userInput.toInt()
  var trows:Int
  var k:Int
  var num:Int

  trows=2*columns-1
  k=1
  for(i in 1..trows) {
    num=1
    for(j in 1..k) {
      print(num++ +" ")
    }

    if(i<columns)k++;
    else k--;

    println("")
  }
}

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

  println("");
}