https://www.acmicpc.net/problem/2446
import 'dart:io';
void main(){
int? n=int.parse(stdin.readLineSync()!);
for(var i=n;i>=1;i--){
var res="";
for(var j=0;j<n-i;j++) res+=" ";
for(var j=0;j<(i-1)*2+1;j++) res+="*";
print(res);
}
for(var i=2;i<=n;i++){
var res="";
for(var j=0;j<n-i;j++) res+=" ";
for(var j=0;j<(i-1)*2+1;j++) res+="*";
print(res);
}
}