Pascal's Triangle in Python (with semi-decent printing)
Today, I ran across a Hacker News thread where someone mentioned that they often ask job applicants to whiteboard a function that would return a row of Pascal's Triangle. I couldn't resist, so and came up with this:
print "\n"
print "Printing Pascal's triangle."
num_rows = input("How many rows do you want: ")
def triangle(num_rows):
width = 2*num_rows - 1
prev_row = []
triangle = []
for row_num in range(num_rows):
row_width = row_num + 1 # the number of items that will appear in this row
if row_num == 0:
row = [1]
else:
row = []
for i in range(row_width):
if i == 0 or i == row_width-1:
# the '1's on either end of each row
row.append(1)
else:
# Calculate the sum of the two numbers above this position
row.append(prev_row[i-1] + prev_row[i])
prev_row = row
triangle.append(row)
return triangle
# Actually generate the triangle
triangle = triangle(num_rows)
# Now print it out nicely
# First, get the width of the last row in the triangle (printed as a string)
width = len(" ".join(["%s" % num for num in triangle[-1]]))
for line in triangle:
print str.center(" ".join(["%s" % num for num in line]), width)Obviously, I was less interested in returning the row as I was in building the triangle itself and printing it. Returning the actual row is left as an exercise to the reader.