https://www.acmicpc.net/problem/2446
using System;
class Program
{
static void Main() {
int n=int.Parse(Console.ReadLine());
for(int i=n;i>=1;i--){
for(int j=0;j<n-i;j++) Console.Write(" ");
for(int j=0;j<(i-1)*2+1;j++) Console.Write("*");
Console.WriteLine();
}
for(int i=2;i<=n;i++){
for(int j=0;j<n-i;j++) Console.Write(" ");
for(int j=0;j<(i-1)*2+1;j++) Console.Write("*");
Console.WriteLine();
}
}
}