再次受到编程101任务的启发，这是另一个挑战。

输入：

• 一个正整数n >= 3。（必须是奇怪的）

输出：

• n星号行，其中第一行有n星号，每条新行都比前一行少两个星号。直到打1星号。从那里开始，每个新行都比之前的行多两个星号，直到回到n星号为止。空格或类似空格之类的东西必须用于对齐星号，以使其看起来真的像沙漏。

一般规则：

• 尾随换行符是允许的，但不必使用。
• 缩进是必须的。
• 这是代码高尔夫球，因此最短答案以字节为单位。
• 由于该课程是用C ++讲授的，所以我很想看到C ++的解决方案。

测试案例（n = 5）：

*****
 ***
  *
 ***
*****

木炭，6个字节

Ｇ↘←↗Ｎ*

死了很简单。绘制聚ģ上的*，与从输入侧采取长度Ñ棕土，其中该侧面下去，右，水平向左，和上-右：

*   *
 * *
  *
 * *
*****

然后自动完成轮廓并填充。

*****
 ***
  *
 ***
*****

在线尝试！

Python 2，57字节

N=n=input()
exec"print('*'*max(n,2-n)).center(N);n-=2;"*n

完整的程序。一行一行，打印正确数量的星号居中。

递归函数较长（67个字节）：

f=lambda n,p='':p+n*'*'+'\n'+(1%n*' 'and f(n-2,p+' ')+p+n*'*'+'\n')

要么

f=lambda n,p='':1/n*(p+'*\n')or f(n-2,p+' ').join([p+n*'*'+'\n']*2)

V，12个字节

Àé*hòl3Äjxx>

在线尝试！

我喜欢这样的挑战，因为我要炫耀V的2D本质的优势。说明。首先，我们需要创建一个由n个星号组成的字符串。因此，我们这样做：

À           " Arg1 times:
 é          " Insert the following single character:
  *         " '*'

附带说明，这直接等同@ai*<esc>于vim，并且寄存器@a已预先初始化为“ arg1”。这使数字输入更加方便。

然后，使用来向右移动字符h。这是有趣的部分：

ò           " Until an error is thrown:
 l          "   Move one character to the right. This will throw an error on anyline with only one asterisk in it
  3Ä        "   Make 3 copies of this line
    j       "   Move down one line
     xx     "   Delete two characters
       >    "   Indent this line once.

现在从技术上讲，这最后一部分是

òl3Äjxx>>ò

因为indent命令实际上是>>。V方便地假定不完整的命令适用于当前行，并且还隐式填充第二个ò字符以进行循环。

C ++元模板，186个字节

使用我的C答案中的显式公式，元模板正在竞争！

template<int N,int X=N*N+N-1>struct H{enum{I=X/(N+1)-N/2,J=X%(N+1)-N/2-1};S s{(J==-N/2-1?'\n':((I>=J&I>=-J)|(I<=J&I<=-J)?'*':' '))+H<N,X-1>().s};};template<int N>struct H<N,-1>{S s="";};

取消高尔夫：

using S=std::string;

template <int N, int X=N*N+N-1>
struct H{
 enum{I=X/(N+1)-N/2,J=X%(N+1)-N/2-1};
 S s{(J==-N/2-1 ? '\n' : ( (I>=J&I>=-J)|(I<=J&I<=-J) ?'*':' '))+H<N,X-1>().s};
};

template <int N> struct H<N,-1> {S s="";}; 

用法：

std::cout << H<5>().s;

不竞争

只是为了好玩：

//T: Tuple of chars
template <char C, char...Tail> struct T { S r=S(1,C)+T<Tail...>().r; };

//specialization for single char
template <char C> struct T<C> { S r=S(1,C); };

//M: Repeated char
template <int N, char C> struct M { S r=S(N,C); };

//U: concatenates T and M
template <class Head, class...Tail> struct U { S r=Head().r+U<Tail...>().r; };

//specialization for Tail=M
template <int N, char C> struct U<M<N,C>> { S r{M<N,C>().r}; };

//specialization for Tail=T
template <char...C> struct U<T<C...>> { S r=T<C...>().r; };

//finally the Hourglass
template <int N, int I=0> struct H {
 S s=U<
       M<I,' '>,
       M<N,'*'>,
       T<'\n'>
      >().r;
 S r{s + H<N-2,I+1>().r + s};
};

//specialization for recursion end
template <int I> struct H<1,I> {
 S r=U<
       M<I,' '>,
       T<'*','\n'>
      >().r;
};

用法：

std::cout << H<5>().r;

PowerShell v2 +，54个字节

param($n)$n..1+2..$n|?{$_%2}|%{" "*(($n-$_)/2)+"*"*$_}

接受输入$n（保证是一个奇数整数），用$n..1和构造两个范围2..$n并将它们连接在一起，然后用来Where-Object仅选择奇数|?{$_%2}。这些被送入一个循环。每次迭代，我们都构造适当数量的空格，并用适当数量的星号将其字符串连接。这些字符串留在管道上，并Write-Output在程序完成时通过隐式插入在它们之间输出换行符。

例子

PS C:\Tools\Scripts\golfing> 3,5,7|%{.\draw-an-hourglass.ps1 $_;""}
***
 *
***

*****
 ***
  *
 ***
*****

*******
 *****
  ***
   *
  ***
 *****
*******

Python，78个字节

所以只有缩进：

f=lambda n,i=0:n>1and' '*i+'*'*n+'\n'+f(n-2,i+1)+' '*i+'*'*n+'\n'or' '*i+'*\n'

用法：

print f(5)

C，114个 109字节

i,j;k(n){for(i=-n/2;i<=n/2;++i)for(j=-n/2;j<=n/2+1;++j)putchar(j==n/2+1?10:(i>=j&i>=-j)|(i<=j&i<=-j)?42:32);}

松散：

i,j;
k(n){
 for(i=-n/2;i<=n/2;++i)
  for(j=-n/2;j<=n/2+1;++j)
   putchar(j==n/2+1?10:(i>=j&i>=-j)|(i<=j&i<=-j)?42:32);
}

先前的递归解决方案：

p(a,c){while(a--)putchar(c);}
f(n,i){p(i,32);p(n,42);p(1,10);}
g(n,i){if(n>1)f(n,i),g(n-2,i+1);f(n,i);}
h(n){g(n,0);}

JavaScript（ES6），66个字节

f=(n,s="*".repeat(n))=>n>1?s+`
`+f(n-2).replace(/^/gm," ")+`
`+s:s

这里的想法是从前一个沙漏生成每个沙漏：在每行的开头添加一个空格，并在n星号前面和后面加上星号。

05AB1E，21 20 19 17字节

借助carusocomputing，节省了2个字节

;ƒ'*¹N·-×Nð×ì})û»

在线尝试！

说明

;ƒ                   # for N in [0 ... floor(input/2)+1]
  '*                 # push an asterisk
    ¹N·-×            # repeat the asterisk input-N*2 times
         Nð×ì        # prepend N spaces
             }       # end loop
              )      # wrap stack in a list
               û     # palendromize
                »    # join with newlines

MATL，12字节

Q2/Zv&<~42*c

在线尝试！

说明

这利用了最近添加的 对称范围函数。

Q     % Input n implicitly. Add 1
      % STACK: 6
2/    % Divide by 2
      % STACK: 3
Zv    % Symmetric range
      % STACK: [1 2 3 2 1]
&<~   % Matrix of all pairwise "greater than or or equal to" comparisons
      % STACK: [1 1 1 1 1
                0 1 1 1 0
                0 0 1 0 0
                0 1 1 1 0
                1 1 1 1 1]
42*   % Multiply by 42 (ASCII code of '*')
      % STACK: [42 42 42 42 42
                 0 42 42 42  0
                 0  0 42  0  0
                 0 42 42 42  0
                42 42 42 42 42]
c     % Convert to char. Implicitly display, with char 0 shown as space
      % STACK: ['*****'
                ' *** '
                '  *  '
                ' *** '
                '*****']

PHP, 95 bytes

for($c=str_pad,$m=$n=$argv[1];$n<=$m;$n+=$d=$d>0||$n<2?2:-2)echo$c($c('',$n,'*'),$m,' ',2)."
";

Instead of storing the rows in an array and then outputting everything, the for loop goes down until 1, and then goes back up to the original number.

C++11, 93 bytes

#include<string>
using S=std::string;S f(int n,int i=0){S s=S(i,32)+S(n,42)+'\n';return n>1?s+f(n-2,i+1)+s:s;}

Slightly ungolfed:

std::string f(int n,int i=0){
 auto s=std::string(i,' ') + std::string(n,'*') + '\n';
 return n>1 ? s+f(n-2,i+1)+s : s;
}

Usage:

std::cout << f(5);

MATL, 20 bytes

XyY>t1X!*t2X!+ZS42*c

Try it online!

R, 77 bytes

M=matrix(" ",n<-scan(),n);for(i in 1:n)M[i:(n-i+1),i]="*";cat(M,sep="",fill=n)

Creates a character matrix, which it then prints out via cat, with fill=n making sure the lines align properly. Note that elements are stored in a matrix column-first (i.e the first two elements are M[1,1] and M[2,1], not M[1,2].)

Java 7, 170 165 164 bytes

Thanks to @Hypino for saving 5 bytes.
Thanks to Kevin for saving 1 byte.

String c(int n,int x){String s,c,t=c=s=" ";int i=0;for(;i++<n;s+="*");for(i=x;i-->=0;c+=" ");for(i=x;i-->0;t+=" ");return(n=n-2)>=0?s+"\n"+c+c(n,++x)+"\n"+t+s:"*";} 

PHP - 95 bytes

$c=2;for($i=$a=$argv[1];$i<=$a;$i-=$c*=$i<2?-1:1)echo str_pad(str_repeat("*",$i),$a," ",2)."
";

Saved a byte by using an actual new line instead of an "\r"

Pyth, 22 bytes

j+J.e+*dk*b\*_:1hQ2_PJ

A program that takes input of an integer on STDIN and prints the result.

Try it online

How it works

j+J.e+*dk*b\*_:1hQ2_PJ  Program. Input: Q
              :1hQ2     Range from 1 to Q+1 in steps of 2. Yields [1, 3, 5, ..., Q]
             _          Reverse
   .e                   Enumnerated map with b as elements and k as indices:
      *dk                 k spaces
         *b\*             b asterisks
     +                    Concatenate the spaces and asterisks
  J                     Store in J
                    PJ  All of J except the last element
                   _    Reverse
 +                      Concatenate J and its modified reverse
j                       Join on newlines
                        Implicitly print

C, 195 191 Bytes

Should golf down a bit smaller

x,y,i;f(n){for(i=0;i<n;i+=2,puts("")){for(y=n-i;y<n;y+=2,putchar(32));for(x=i;x++<n;putchar(42));}for(i=n-2;~i;i-=2,puts("")){for(y=n-i+2;y<n;y+=2,putchar(32));for(x=i-1;x++<n;putchar(42));}}

We can test it here on ideone

C, 79 bytes

h(m,n,k){for(n=m++,k=n*m;--k;putchar(k%m?abs(k%m-m/2)>abs(k/m-n/2)?32:42:10));}

It splits the countdown variable k into row and column indices. If the column index is 0 (last char in a row), it outputs a newline character (10). Then it adjusts the row and column indices to be around the center asterisk. Then, abs(x) < abs(y) is a short condition for outputting a space.

Ruby, 55 54 bytes

f=->n,s=0{puts a=' '*s+?**n;(f[n-2,s+1];puts a)if n>1}

Java 7, 156 bytes

Fairly simple. Keeps track of lines with n, stars with j, spaces with s, and direction with d. I really just wanted a non-recursive Java answer on the board, but it doesn't hurt that it's also a bit shorter :)

String f(int n){String o="";int j=n,s=0,i,d=0;for(;n-->0;o+="\n"){for(i=0;i++<s;)o+=" ";for(i=0;i++<j;)o+="*";d+=j<2?1:0;j+=d<1?-2:2;s+=d<1?1:-1;}return o;}

With line breaks:

String f(int n){
    String o="";
    int j=n,s=0,i,d=0;
    for(;n-->0;o+="\n"){
        for(i=0;i++<s;)
            o+=" ";
        for(i=0;i++<j;)
            o+="*";
        d+=j<2?1:0;
        j+=d<1?-2:2;
        s+=d<1?1:-1;
    }
    return o;
}

APL, 19 bytes

' *'[1+∘.≤⍨(⊢⌊⌽)⍳⎕]

Test:

      ' *'[1+∘.≤⍨(⊢⌊⌽)⍳⎕]
⎕:
      5
*****
 *** 
  *  
 *** 
*****

Explanation:

                 ⎕   ⍝ read number  
                ⍳    ⍝ 1..N
           ( ⌊ )     ⍝ at each position, minimum of
            ⊢        ⍝ 1..N
              ⌽      ⍝ and N..1 (this gives 1..N/2..1)
       ∘.≤⍨          ⍝ outer product with ≤
     1+              ⍝ add 1 to each value
' *'[             ]  ⍝ 1→space, 2→asterisk

Haskell, 84 bytes

f n|l<-div n 2,k<-[-l..l]=putStr$unlines[[" *"!!(fromEnum$abs x<=abs y)|x<-k]|y<-k]

C (gcc), 80 74 bytes

Thank ceilingcat for 6 bytes

-Du(x,k)=for(x=~n;x+=2,x<n;putchar(k))

i;j;f(n){u(i,10)u(j,i*i<j*j?32:42);}

Try it online!

PowerShell, 54 50 bytes

filter f{if($_-1){'*'*$_;($_-2)|f|%{" $_"}}'*'*$_}

Try it online!

PHP, 104 88 bytes

for(;$i++<$argn;$a.='**',$i++>1?$o=$s.$o:1)$o.=$s=str_pad("*$a",$argn,' ',2)."
";echo$o;

Try it online!

This doesn't beat the lowest scores for PHP on this challenge, but it's just too crazy for me to throw away.

Okay, so I've golfed now it to be the (not for long) lowest score for PHP on this challenge, but it doesn't change the fact that it's still crazy.

$ echo 7|php -nF hour.php
*******
 *****
  ***
   *
  ***
 *****
*******

Groovy, 66 Bytes

{n->((n..1)+(2..n)).each{if(it%2>0){println(("*"*it).center(n))}}}

Try it: https://groovyconsole.appspot.com/script/5145735624392704

Explained:

((n..1)+(2..n)) - Reverse palindromize to n [n,..,1,..,n]

.each{if(it%2>0){...} - Iterate through odd elements.

println(("*"*it).center(n)) - Center n stars and print each on newline.

PHP, 191 bytes

$b=[];for($i=$a=$argv[1]+1;$i>0;$i--){$i--;if($i<=1){$c=str_pad("*",$a," ",2)."\n";break;}$b[]=str_pad(str_repeat("*",$i),$a," ",2)."\n";}echo implode("",$b).$c.implode("",array_reverse($b));

Run like php -f golf_hourglass.php 15

# php -f golf_hourglass.php 15
***************
 *************
  ***********
   *********
    *******
     *****
      ***
       *
      ***
     *****
    *******
   *********
  ***********
 *************
***************

The idea behind it is to create the top half (the part before the single *), then just echo the top part twice, but the second time in reverse order.

Pyke, 22 19 bytes

F-ed*ih\**+)2%'X_OX

Try it here!

F          )        -    for i in range(input)
 -                  -        Q-i
  e                 -       floor(^/2)
   d*               -      ^*" "
          +         -     ^+V
     ih             -       i+1
       \**          -      ^*"*"
            2%      -   ^[::2]
              'X_   - splat(^),
                       reversed(^)
                 OX - splat(^[:-1])

C, 117 bytes

void p(c,n){while(n--)putchar(c);}void h(n){for(int i=n;i>=-n;i-=i==1?4:2){p(32,(n-abs(i))/2);p(42,abs(i));p(10,1);}}

Ungolfed

void printNum(c, n) {
  while (n--)
    putchar(c);
}

void hourGlass(n) {
  for (int i = n; i >= -n; i-=i==1?4:2) {
    printNum(32, (n - abs(i)) / 2);
    printNum(42, abs(i));
    printNum(10, 1);
  }
}