Asterisk triangle in python [duplicate]

问题

I have to write a recursive function asterisk_triangle which takes an integer and then returns an asterisk triangle consisting of that many lines.

For e.g this is a 4 line asterisk triangle.

*
**
***
****

I came up with this function:

def asterisk_triangle(n):
    """
    takes an integer n and then returns an
    asterisk triangle consisting of (n) many lines
    """
    x = 1
    while (x <= n):
        print("*" * x)
        x = x + 1
    return

And also I had to create an upside down asterisk triangle by manipulating the first function.

I came up with this function and result:

def upside_down_asterisk_triangle(n):
     """
     takes an integer n and then returns a backwards
     asterisk triangle consisting of (n) many lines
     """
     x = 0
     while (x < n):
          print("*" * (n-x))
     x = x + 1
     return


****
***
**
*

Now I have to manipulate these functions to create a backwards asterisk triangle.

   *
  **
 ***
****

And a backward upside down asterisk triangle.

****
 ***
  **
   *

What functions should I implement?

I have tried using the reverse string command [::-1] after the function and it didn't work.

回答1:

I already answered the same question earlier. Keep in mind that none of the functions you mentioned are recursive functions. You can read more about recursion here.

This is the example I mentioned here.

Python 3.X

def asterix_triangle(i, t=0):
    if i == 0:
        return 0
    else:
        print(' ' * ( i + 1 ) + '*' * ( t * 2 + 1 ))
        return asterix_triangle( i - 1, t + 1 )

asterix_triangle(5)

And here you have an upside down version of an recursive function.

def upside_down_asterix_triangle(i, t=0):
    if i == 0:
        return 0
    else:
        print(' ' * ( t + 1 ) + '*' * ( i * 2 - 1 ))
        return upside_down_asterix_triangle( i - 1, t + 1 )

upside_down_asterix_triangle(5)

Python 2.X

def asterix_triangle(i, t=0):
    if i == 0:
        return 0
    else:
        print ' ' * ( i + 1 ) + '*' * ( t * 2 + 1 )
        return asterix_triangle( i - 1, t + 1 )

asterix_triangle(5)

And here you have an upside down version of an recursive function.

def upside_down_asterix_triangle(i, t=0):
    if i == 0:
        return 0
    else:
        print ' ' * ( t + 1 ) + '*' * ( i * 2 - 1 )
        return upside_down_asterix_triangle( i - 1, t + 1 )

upside_down_asterix_triangle(5)

Edit: Screenshot showing the script running in my IDE.

Edit2: Added code that works under Python 3.x

Edit3: Added iterative function for Python 3.X

def create_pyramid(rows):
    for i in range(rows):
        print((' ' * ( rows- i - 1 ) + '*' * ( 2 * i + 1)))

print((create_pyramid(5)))

def create_upside_down_pyramid(rows):
    for i in reversed(list(range(rows))):
        print((' ' * ( rows- i - 1 ) + '*' * ( 2 * i + 1)))

print((create_upside_down_pyramid(5)))

来源：https://stackoverflow.com/questions/15560730/asterisk-triangle-in-python

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