题解

#include<cstdio>
#include<iostream>
#include<cmath>
using namespace std;
int main(){
	int a;
    cin>>a;
    char x='*';
    for(int i=1;i<=a;i++){
        for(int j=i;j<=a-1;j++){
            cout<<" ";
        }
        for(int j=1;j<=i*2-1;j++){
            if(j==1||j==i*2-1)cout<<x;
        	else cout<<" ";
        }
        cout<<endl;
    }
    for(int i=a-1;i>=1;i--){
        for(int j=a-1;j>=i;j--){
            cout<<" ";
        }
        for(int j=1;j<=i*2-1;j++){
        	if(j==1||j==i*2-1)cout<<x;
        	else cout<<" ";
        }
        cout<<endl;
    }
	return 0;
}