- Input: Integer `n`
- Output: String

Example:

`a(4)` prints as
```
   A   
  A A  
 A A A 
A     A
```

`a(8)` prints as
```
       A       
      A A      
     A   A     
    A     A    
   A A A A A   
  A         A  
 A           A 
A             A
```

`a(12)` prints as
```
           A           
          A A          
         A   A         
        A     A        
       A       A       
      A         A      
     A A A A A A A     
    A             A    
   A               A   
  A                 A  
 A                   A 
A                     A
```
Note:

- Each line's length is `2n - 1`
- Each line should be concatenate by line break `"\n"`
- If `n` is less than `4`, it should return `""`
- If `n` is odd, `a(n) = a(n - 1)`, eg `a(5) == a(4); a(9) == a(8)`

Difficulty: introductory

Starter code:

def a(n):
	

Solutions:
def a(n):
    """
    """
    if n % 2 != 0:
        n = n - 1
    if n < 4:
        return ''
    side = " " * (n - 1)
    li = [side + "A" + side]
    for i in range(1, n):
        side = side[1:]
        middle = "A " * (i - 1) if i == (n / 2) else "  " * (i - 1)
        li.append(side + "A " + middle + "A" + side)
    return "\n".join(li)

def a(n):
    if n < 4:
        return ""
    if n % 2:
        n -= 1
    lines = (
        "A" if i == 0 else
        " ".join("A" * (i + 1)) if i == n // 2 else
        "A" + " " * (2 * i - 1) + "A"
        for i in range(n)
    )
    width = 2 * n - 1
    return "\n".join(line.center(width) for line in lines)

def a(n):
    n -= n%2
    if n<4: return ''
    return '\n'.join( '{0}{1}{0}'.format('A' * (i%(n//2) != 0),
                                         ' ' * (i*2-1) if i%(n//2) else ' '.join( ['A']*(i+1) )
                                        ).center(2*n-1) for i in range(n) )

def a(n):
    n = n if n % 2 == 0 else n - 1
    width = 2 * n - 1
    lines = ["A".center(width)] + [("A" + " "*k + "A").center(width) for k in range(1, n-1, 2)] +\
        [" ".join(["A"]*(n//2+1)).center(width)] + [("A" + " "*k + "A").center(width) for k in range(n+1, 2*n-1, 2)]
    return "\n".join(lines) if n >= 4 else ""

def a(n):
    if n<4: return ''
    n-=n%2
    l=2*n-1
    return '\n'.join((' '.join(['A']*(i+1)) if i*2==n else ''.join('A' if j in (0,i*2) else ' ' for j in range(i*2+1))).center(l) for i in range(n))

a=lambda n:"\n".join(['A'.center(2*(n-(n&1))-1)]+[[(("A "*((n-(n&1))//2+1)).rstrip()).center(2*(n-(n&1))-1),("A"+(" "*(i*2+1))+"A").center(2*(n-(n&1))-1)][i!=(n-(n&1))//2-1]for i in range(n-1-(n&1))])if n-(n&1)>3 else ""