Create a function hollow_triangle(height) that returns a hollow triangle of the correct height. The height is passed through to the function and the function should return a list containing each line of the hollow triangle. 
```
hollow_triangle(6) should return : ['_____#_____', '____#_#____', '___#___#___', '__#_____#__', '_#_______#_', '###########']
hollow_triangle(9) should return : ['________#________', '_______#_#_______', '______#___#______', '_____#_____#_____', '____#_______#____', '___#_________#___', '__#___________#__', '_#_____________#_', '#################']
```
The final idea is for the hollow triangle is to look like this if you decide to print each element of the list: 
``` 
hollow_triangle(6) will result in:
_____#_____              1
____#_#____              2
___#___#___              3
__#_____#__              4
_#_______#_              5
###########              6 ---- Final Height

hollow_triangle(9) will result in:
________#________        1
_______#_#_______        2
______#___#______        3
_____#_____#_____        4      
____#_______#____        5
___#_________#___        6
__#___________#__        7
_#_____________#_        8
#################        9 ---- Final Height
```
Pad spaces with underscores i.e _ so each line is the same length.Goodluck and have fun coding !

Difficulty: introductory

Starter code:

def hollow_triangle(n):
	

Solutions:
def hollow_triangle(n):
    width = n * 2 - 1
    row = '{{:_^{}}}'.format(width).format
    return [row(mid(a)) for a in xrange(1, width, 2)] + [width * '#']


def mid(n):
    return '#' if n == 1 else '#{}#'.format('_' * (n - 2))

def hollow_triangle(n):
    w, result = 2 * n - 1, [f"{'_' * (2*i-1):#^{2*i+1}}" for i in range(n - 1)]
    return [f"{l:_^{w}}" for l in result] + ["#" * w]

hollow_triangle=lambda n:["".join([['_','#'][k in[n-1-i,n-1+i]]for k in range(n*2-1)])for i in range(n-1)]+[f"{'#'*(n*2-1)}"]

def hollow_triangle(n):
  return [(f'#{"_" * (2*i-1)}#' if i else '#').center(2*n-1, '_') for i in range(n-1)] + ['#' * (2*n-1)]

def hollow_triangle(n):
    return ['_' * (n - i - 1) + '#' + '_' * (2 * i - 1) + '#' * (i >= 1) + '_' * (n - i - 1) \
    for i in range(n - 1)] + ['#' * (2 * n - 1)]

def hollow_triangle(n):
    if n == 1:
        return ['#']
    first = ["_"*(n-1)+"#"+"_"*(n-1)]
    last = ["#"*(2*n-1)]
    return first +["_"*(n-i-1)+"#"+"_"*(2*i-1)+"#"+"_"*(n-i-1) for i in range(1,n-1)] + last

def hollow_triangle(n):
    total_width = 2 * n - 1
    triangle = ['#'.center(total_width, '_')]
    for i in range(1, total_width-2, 2):
        triangle.append('#{}#'.format('_' * i).center(total_width, '_'))
    triangle.append('#' * total_width)
    return triangle

m,hollow_triangle=lambda s:s[:0:-1]+s,lambda n:[m('_'*i+'#'+'_'*(n-i-1))for i in range(n-1)]+[m(n*'#')]

def hollow_triangle(n):
    lines = ['_' * (n-i-1) + '#' + '_' * (2*i-1) + '#' + '_' * (n-i-1) for i in range(1, n-1)]
    return ['_' * (n-1) + '#' + '_' * (n-1)] + lines + ['#' * (2*n-1)] if n > 1 else ['#']

def hollow_triangle(n):
    ans = []
    for i in range(n-1, 0, -1):
        x = '_' * i + '#' + '_' * (n-i-1)
        ans.append(x[:-1] + x[::-1])
    return ans + ['#' * (2*n - 1)]