Print Pascal's Triangle in Python properly

Question

I have coded a Pascal's Triangle program in Python but the triangle is printing as a right angled triangle

n=int(input("Enter the no. of rows: "))
for line in range(1, n + 1):  
    c = 1   
    x=n 
    y=line  

    for i in range(1, line + 1): 
    
        print(c, end = " ")
        c = int(c * (line - i) / i)
    print(" ")

This gives the output as

Enter the no. of rows: 5
1
1 1
1 2 1
1 3 3 1
1 4 6 4 1

But I want it like this

You don't need to rewrite a bunch of code. this gets solved by just adding 1 line to the code and a small modification to another line (both print statements). check my answer for a minimal delta solution. — Akshay Sehgal, Dec 22 '20 at 05:56

score 4 · Answer 1 · answered Dec 22 '20 at 05:12

Rather than use a fixed number width, let's try to make the triangle self-adjust:

rows = int(input("Enter the no. of rows: "))

triangle = []

for row in range(1, rows + 1):
    c = 1

    numbers = []

    for i in range(1, row + 1):
        numbers.append(c)
        c = c * (row - i) // i

    triangle.append(numbers)

last_row = triangle[-1]
number_width = len(str(max(last_row))) + 1
triangle_width = number_width * len(last_row)

for row in triangle:
    string = ""

    for number in row:
        number_string = str(number)
        string += number_string + ' ' * (number_width - len(number_string))

    print(string.center(triangle_width))

And take advantage of that str.center() method! Adjust spacing as you see fit.

OUTPUT

> python3 test.py
Enter the no. of rows: 10
                  1                     
                1   1                   
              1   2   1                 
            1   3   3   1               
          1   4   6   4   1             
        1   5   10  10  5   1           
      1   6   15  20  15  6   1         
    1   7   21  35  35  21  7   1       
  1   8   28  56  70  56  28  8   1     
1   9   36  84  126 126 84  36  9   1   
>

This is best for centering. Even if rows=20. – Warren Van Wyck Jun 27 '23 at 23:45 — Warren Van Wyck, Jun 27 '23 at 23:45

score 2 · Accepted Answer · answered Dec 22 '20 at 05:54

You could simply just modify your existing code with 2 modifications -

Before each line, add (n-line) spaces
Center align each of the 1 or 2 digit numbers into a 4 alphabet space (changing this yields interesting skewed results :))

n=8
for line in range(1, n + 1):  
    c = 1   
    x=n
    y=line
    #######
    print("  "*(n-line), end="") #This line adds spaces before each line
    #######
    for i in range(1, line + 1): 
        ########
        print(str(c).center(4), end = "") #This center aligns each digit
        ########
        c = int(c * (line - i) / i)
    print(" ")

               1   
             1   1   
           1   2   1   
         1   3   3   1   
       1   4   6   4   1   
     1   5   10  10  5   1   
   1   6   15  20  15  6   1   
 1   7   21  35  35  21  7   1

score 0 · Answer 3 · answered Dec 22 '20 at 04:33

n=int(input("Enter number of rows: "))
a=[]
for i in range(n):
    a.append([])
    a[i].append(1)
    for j in range(1,i):
        a[i].append(a[i-1][j-1]+a[i-1][j])
    if(n!=0):
        a[i].append(1)
for i in range(n):
    print("   "*(n-i),end=" ",sep=" ")   
    for j in range(0,i+1):
        print('{0:6}'.format(a[i][j]),end=" ",sep=" ")
    print()

The line print(" "*(n-i),end=" ",sep=" ") gives the initial spaces you are looking for.

Print Pascal's Triangle in Python properly

3 Answers3

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