Draw an hourglass

Question

Again inspired by a task for Programming 101 here's another challenge.

Input:

• A positive integer n >= 3. (has to be odd)

Output:

• n lines of asterisks, where the first line has n asterisks and every new line has two asterisks less than the line before. Until hitting 1 asterisk. From there every new line has two asterisks more than the line before until getting back to n asterisks. Spaces or something like spaces have to used to align the asterisks so that it really will look like an hourglass.

General rules:

• Trailing newlines are allowed but do not have to be used.
• indentation is a must.
• This is code-golf, so shortest answer in bytes wins.
• Since the course is taught in C++, I'm eager to see solutions in C++.

Test case (n=5):

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

Answer 1

Charcoal, 6 bytes

Ｇ↘←↗Ｎ*

Dead simple. Draw a polyGon of *, with side length taken from an input Number, where the sides go down-and-right, horizontally left, and up-and-right:

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

Then autocomplete the outline and fill it.

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

Try it online!

Answer 2

Python 2, 57 bytes

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

A full program. Goes line by line, printing the right number of asterisks centered.

A recursive function was longer (67 bytes):

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

or

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

Answer 3

V, 12 bytes

Àé*hòl3Äjxx>

Try it online!

I like challenges like this because I get to show off the advantages of V's 2D nature. Explanation. First, we need to create a string of n asterisks. So, we do this:

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

As a side note, this is directly equivalent to @ai*<esc> in vim, and register @a is pre-initialized to "arg1". This makes numeric input much more convenient.

Then, we move on character to the right with h. Here is the fun part:

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.

Now technically, this last part is

òl3Äjxx>>ò

Because the indent command is actually >>. V conveniently assumes incomplete commands apply to the current line, and also implicitly fills in the second ò character for looping.

Answer 4

C++ Metatemplates, 186 bytes

With the explicit formula from my C answer the Metatemplates are competing!

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="";};

Ungolfed:

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="";}; 

usage:

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

non-competing

Just for the sake of fun:

//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;
};

Usage:

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

Answer 5

PowerShell v2+, 54 bytes

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

Takes input $n (guaranteed to be an odd integer), constructs two ranges with $n..1 and 2..$n and concatenates them together, then uses Where-Object to select only the odd ones with |?{$_%2}. Those are fed into a loop. Each iteration, we construct the appropriate number of spaces, string-concatenated with the appropriate number of asterisks. Those strings are left on the pipeline, and output via implicit Write-Output inserts newlines between them at program completion.

Examples

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

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

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

Answer 6

Python, 78 bytes

So only with indentation:

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

Usage:

print f(5)

Answer 7

C, 114 109 bytes

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);}

ungolfed:

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);
}

Previous recursive solution:

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);}

Answer 8

JavaScript (ES6), 66 bytes

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

The idea here is to generate each hourglass from the previous: add a space at the beginning of every line, and both prepend and append n asterisks.

Answer 9

05AB1E, 21 20 19 17 bytes

Saved 2 bytes thanks to carusocomputing

;ƒ'*¹N·-×Nð×ì})û»

Try it online!

Explanation

;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

Answer 10

MATL, 12 bytes

Q2/Zv&<~42*c

Try it online!

Explanation

This makes use of the recently added symmetric range function.

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: ['*****'
                ' *** '
                '  *  '
                ' *** '
                '*****']

Answer 11

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.

Answer 12

PowerShell, 54 50 bytes

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

Try it online!

Answer 13

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

Answer 14

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);

Answer 15

MATL, 20 bytes

XyY>t1X!*t2X!+ZS42*c

Try it online!

Answer 16

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:"*";} 

Answer 17

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].)

Answer 18

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"

Answer 19

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!

Answer 20

Canvas, 7 bytes

⇵｛*×］⤢┼

Try it here!

Explanation:

⇵｛*×］⤢┼
⇵         ceiling divide by 2
 ｛  ］    map over [1..pop]
   *         push *
    ×        repeat by the counter
       ⤢  transpose
        ┼  quad-palindromize with 1 overlap

+1 byte with support for even numbers

Answer 21

J, 30 28 bytes

-2 bytes thanks to FrownyFrog!

' *'{~[:(>.|.)@(*|."1)]\@#&1

Try it online!

Answer 22

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

Answer 23

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

Answer 24

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.

Answer 25

Ruby, 55 54 bytes

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

Answer 26

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;
}

Answer 27

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

Answer 28

Haskell, 84 bytes

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

Answer 29

Common Lisp, 101 bytes

(dotimes(i(1+(set'x(read))))(format t"~v:@<~v{*~}~>~&"x(set'b(abs(- x(* i 2))))1)(if(= 1 b)(incf i)))

Answer 30

Excel VBA, ₆₈ 67 Bytes

Anonymous VBE immediate window function that takes input from [A1] and outputs to the VBE immediate window

n=[Int(A1/2)]:For i=-n To n:j=abs(i):?Spc(n-j)String(2*j+1,42):Next

Answer 31

SOGL V0.12, 12 bytes

.↔∫ **}⁰№§╬3

Try it Here!

Answer 32

Ruby, 66 bytes

->n{(-n..n).each{|x|x.abs>1?(puts"*"*x.abs):(puts"*"*x if x>0)}}

Probably a shorter way of doing this, but this is the most straight forward one i came up with.

Answer 33

Japt, 11 bytes

õ_î*ÃÔë ê û

Try it online

Answer 34

Japt -R, 11 bytes

1õU2_ç*Ãê û

Try it

                :Implicit input of integer U
1õU2            :Range [U,1] in increments of 2
    _           :Map each Z
     ç*         :  Repeat "*" Z times
       Ã        :End map
        ê       :Palindromise
          û     :Centre pad each element with spaces to the length of the longest
                :Implicitly join with newlines and output

Answer 35

Python 3, 79 bytes

def f(i):[print(' '*(i//2-abs(j-i//2))+'*'*2*abs(j-i//2)+'*')for j in range(i)]

Answer 36

Oracle SQL, 119 bytes

SQL> select lpad(' ',ceil(n/2)-x-1,' ')||rpad('*',x*2+1,'*')from(select n,abs(ceil(n/2)-rownum)x from t connect by level<=n)
  2  /

LPAD('',CEIL(N/2)-X-1,'')||RPAD('*',X*2+1,'*')
--------------------------------------------------------------------------------
*******
 *****
  ***
   *
  ***
 *****
*******

7 rows selected.

Answer 37

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.

Answer 38

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.

Answer 39

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])

Answer 40

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);
  }
}

Answer 41

PHP, 158 bytes

(-2 if I can omit the start tag)

<?$v=$argv[1]/2;while($c++<$v){$a="";$b=$v+.5;while(--$b)$a.=$b<$c?" ":"*";$z[]=strrev($a)."*$a";}$c=array_pop($z);$a=join($z,"
");echo"$a
$c
".strrev($a);

A similar approach to the one @hd took but uses manual concatenation instead of built-in string functions with overly long names. I wish I could call $z->pop()

Answer 42

Pyth, 22 bytes

VQ+*d-J/Q2aJN*\*hatQyN

Try online.

Lame attempt at explaining:

VQ+*d-J/Q2aJN*\*hatQyN   The whole thing.
VQ                       For N in [0,1,2, ... ,Q-1]; Q takes the input.
      J/Q2               Integer division Q/2, store in J
          aJN            Absolute difference between N and J
     -                   Subtract the above numbers...
   *d                    ...and repeat whitespace that many times
  +                      Concatenate that with output from the next block
                 atQyN   Absolute difference between Q-1 and 2*N
             *\*h        Repeat an asterisk the above number of times + 1

Interestingly I matched TheBikingViking's score on the same language using a different approach... O:

Answer 43

Batch, 191 154 bytes

@echo off
set s=*
set l=for /l %%i in (2,1,%1)do call:
%l%s
%l%s
%l%u
%l%l
:l
echo %s%
:s
set s=%s:~1%**
exit/b
:u
echo %s%
set s= %s:~0,-2%

The u subroutine generates the top half of the hourglass by prepending a space and removing two trailing stars each time. The l subroutine generates the bottom half of the hourglass by removing a space and appending two trailing stars each time. The code falls through into the l subroutine at the end to save bytes. The second half of the l subroutine is also used to build up the initial string, although it has to be called twice as many times as the string doesn't have its spaces yet.

Edit: Saved 37 bytes by using an idea by @ConorO'Brien.

Answer 44

Racket 177 bytes

(let p((n N)(d #t))(for((i(/(- N n)2)))(display" "))(for((i n))(display #\*))(displayln"")
(cond[(and(not d)(= n N))][(= n 1)(set! d #f)(p(+ 2 n)d)][d(p(- n 2)d)][(p(+ 2 n)d)]))

Ungolfed:

(define (f N)
  (let loop ((n N)
             (d #t))                      ; descending
    (for ((i (/(- N n)2)))
          (display " "))
    (for ((i n))
      (display #\*))
    (displayln "")
    (cond
      [(and (not d) (= n N))]             ; end
      [(= n 1) (set! d #f)
               (loop (+ 2 n) d)]
      [d (loop (- n 2) d)]
      [(loop (+ 2 n) d)]))
  )

Testing:

(f 9)

Output:

*********
 *******
  *****
   ***
    *
   ***
  *****
 *******
*********
#t

Answer 45

Swift 3, 139 130

let c={String(repeating:$0,count:$1)};func d(_ n:Int,_ i:Int=0)->String{let b=c(" ",i)+c("*",n)+"\n";return n>1 ?b+d(n-2,i+1)+b:b}

On-line test

let c={(s,i)in(0..<i).reduce(""){(b,_)in b+s}};func d(_ n:Int,_ i:Int=0)->String{let b=c(" ",i)+c("*",n)+"\n";return n>1 ?b+d(n-2,i+1)+b:b}

Answer 46

CJam, 26 bytes

ri:A,_W%.e<{_S*A@2*-'**N}/

Try it online!

ri:A     e# read integer, save as A
,_W%     e# make range and mirror (e.g.[0,1,2,3,4],[4,3,2,1,0])
.e<      e# take minimums (e.g.[0,1,2,1,0])
{        e# for each minimum "m"
  _S*    e#   push m spaces
  A@2*-  e#   calculate A-2m (rotates to spare m)
  '**    e#   push A-2m asterisks
  N      e#   push a newline
}/       e# end, prints stack

Answer 47

T-SQL, 93 bytes

This will also provide an answer when an even number is used - the bottom row will be missing.

Golfed:

DECLARE @ INT=5

,@i INT=0z:PRINT SPACE(@/2-abs(@/2-@i))+REPLICATE('*',abs(@/2-@i)*2+1)SET
@i+=1IF @i<@ GOTO z

Ungolfed:

DECLARE @ INT=5

,@i INT=0
z:
PRINT SPACE(@/2-abs(@/2-@i))+REPLICATE('*',abs(@/2-@i)*2+1)
SET @i+=1
IF @i<@ GOTO z

A bit longer alternative solution without looping

USE master
DECLARE @ INT=5
SELECT top(@)SPACE(@/2-abs(@/2-number))+REPLICATE('*',abs(@/2-number)*2+1)
FROM spt_values
WHERE'P'=type

Fiddle

Answer 48

Actually, 34 bytes

;╗R`1&`░`'**╜kd#"{:^%d}"%f`M;pXR+i

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Explanation:

;╗R`1&`░`'**╜kd#"{:^%d}"%f`M;pXR+i
;╗                                  store a copy of n in register 0
  R                                 range(1, n+1) ([1, n])
   `1&`░                            filter: keep only odd values
        `'**╜kd#"{:^%d}"%f`M        for each value:
         '**                          push a string containing that many asterisks
            ╜                         push n
             kd#                      list from stack, dequeue, listify (make both stack elements singleton lists)
                "{:^%d}"%             format string to center string in n-wide field
                         f            do the formatting
                            ;pXR+   duplicate list, discard the extra "*" element, reverse, and append original list (vertical mirroring)
                                 i  flatten and implicitly print