https://www.acmicpc.net/problem/2523
#include <iostream>
using namespace std;
int main() {
int n;
cin>>n;
for(int i=1;i<=n;i++){
for(int j=0;j<i;j++) cout<<"*";
cout<<"\n";
}
for(int i=n-1;i>=1;i--){
for(int j=0;j<i;j++) cout<<"*";
cout<<"\n";
}
}