P2.5.1Pascal's triangle #2
Modify your solution to Problem 2.4.4 to output the first 50 rows of Pascal's triangle, but instead of the numbers themselves, output an asterisk if the number is odd and a space if it is even.
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The code below outputs the required pattern, which is a Sierpinski gasket.
# Output a pattern based on the parity of numbers in Pascal's Triangle
nmax = 50
rows = [[1],[1,1]]
for n in range(2, nmax+1):
rows.append([1,])
# Insert the entries for this row by summing neighbours in the previous row
for k in range(n-1):
rows[n].append(rows[n-1][k]+rows[n-1][k+1])
rows[n].append(1)
# Pretty-print the rows as asterisks for odd numbers or else spaces
for i,row in enumerate(rows):
s_row = []
for x in row:
if x % 2:
s_row.append('*')
else:
s_row.append(' ')
print(''.join(s_row))
The output is:
*
**
* *
****
* *
** **
* * * *
********
* *
** **
* * * *
**** ****
* * * *
** ** ** **
* * * * * * * *
****************
...
The loop printing the asterisks can be expressed more concisely using list comprehension (Section 4.3.2):
for i,row in enumerate(rows):
print(''.join(['*' if x % 2 else ' ' for x in row]))