Solving palindromic 'Triangle Quest' puzzle in Python

Question

I'm trying to solve this programming puzzle:

You are given a positive integer N (0 < N < 10). Your task is to print a palindromic triangle of size N.

For example, a palindromic triangle of size 5 is:
1
121
12321
1234321
123454321
You can't take more than two lines. You have to complete the code using exactly one print statement.

Note: Using anything related to strings will give a score of 0. Using more than one for-statement will give a score of 0.

I can think only of 'dumb' way to do this:

for i in range(1, N+1):
    print([0, 1, 121, 12321, 1234321, 123454321, 12345654321, 1234567654321, 123456787654321, 12345678987654321][i])

Is there a more elegant solution?

Somehow, there is now way to get a non-zero score, as printing is related to strings. — DainDwarf, Dec 28 '15 at 13:21

Alex Aza · Answer 1 · 2018-03-02T07:18:27.720

11

for i in range(1,int(input())+1):
   print(int((10**i-1)/9)**2)

1 -> (   10 - 1) / 9 =    1,    1 *    1 = 1
2 -> (  100 - 1) / 9 =   11,   11 *   11 = 121
3 -> ( 1000 - 1) / 9 =  111,  111 *  111 = 12321
4 -> (10000 - 1) / 9 = 1111, 1111 * 1111 = 1234321

edited Mar 02 '18 at 07:18

answered Mar 02 '18 at 07:12

Alex Aza

76,499
26
155
134

score 10 · Accepted Answer · answered Dec 28 '15 at 13:40

10

I ended up doing the following (thanks @raina77ow for the idea):

for i in range(1, N+1):
    print((111111111//(10**(9-i)))**2)

answered Dec 28 '15 at 13:40

planetp

14,248
20
86
160

7

Slightly better way: `print((10**i//9)**2)`. – simonzack Dec 28 '15 at 13:45

vesche · Answer 3 · 2015-12-28T14:02:45.687

6

for i in range(1,6):
    print (((10 ** i - 1) // 9) ** 2)

Here's a wtf one liner:

f=lambda n:n and[f(n-1),print((10**n//9)**2),range(1,n+1)];f(5)

edited Dec 28 '15 at 14:02

answered Dec 28 '15 at 13:46

vesche

1,842
1
13
19

score 5 · Answer 4 · answered Oct 06 '17 at 02:53

5

def palindrome(N):
    for i in range(1, N + 1):
        print(int('1' * i)**2)

palindrome(int(input()))

1 * 1 = 1
11 * 11 = 121
111 * 111 = 12321

answered Oct 06 '17 at 02:53

noobninja

900
12
14

If the coding challenge rules exclude strings, then this solution will fail. – noobninja Oct 06 '17 at 18:51

score 1 · Answer 5 · answered Jul 08 '20 at 13:03

1

  for i in range(1,int(input())+1): #More than 2 lines will result in 0 score. Do not leave a blank line also
    print(''.join(list(map(lambda x:str(x),list(range(i+1))[1:]))+list(map(lambda x:str(x),list(reversed(list(range(i))[1:]))))))

answered Jul 08 '20 at 13:03

Pravin Kumar

55
5

score 1 · Answer 6 · answered Jul 18 '20 at 19:22

1

This is a simple string-less version:

for i in range(1, int(input()) + 1):
    print(sum(list(map(lambda x: 10 ** x, range(i)))) ** 2)

answered Jul 18 '20 at 19:22

Thomas

11
1

PascalVKooten · Answer 7 · 2015-12-28T14:40:33.460

0

Code golfing and taking advice of simon and rain:

set(map(lambda x:print((10**x//9)**2),range(1,N+1)))

edited Dec 28 '15 at 14:40

answered Dec 28 '15 at 13:48

PascalVKooten

20,643
17
103
160

score 0 · Answer 8 · answered Dec 28 '15 at 13:50

0

for i in range(1, N + 1):
    print(*list(range(1, i + 1)) + list(range(i - 1, 0, -1)), sep = None)

answered Dec 28 '15 at 13:50

Keith Hall

15,362
3
53
71

This separates the numbers by space (and using `sep=""` is not allowed) – planetp Dec 28 '15 at 14:34
@planetp, you are correct that it separates the numbers by space, but the OP didn't specify that separating the numbers by space isn't allowed - after all, the answer is still a palindromic triangle, just with spaces :) however, even if it is not valid, I thought it was worth including because it is potentially more understandable than the math answers :) – Keith Hall Dec 28 '15 at 14:37
Way late to the party, but... ```python reduce(lambda x, y: x*10 + y, list(range(1, i + 1)) + list(range(i - 1, 0, -1))) ``` – chris.guethle Dec 14 '16 at 19:52

score 0 · Answer 9 · answered Jan 15 '16 at 07:47

0

Just because every solution offered so far involves range() which I feel is overused in Python code:

from math import log10

i = 1
while (N > log10(i)): print(i**2); i = i * 10 + 1

answered Jan 15 '16 at 07:47

cdlane

40,441
5
32
81

score 0 · Answer 10 · edited Dec 26 '20 at 14:37

0

I am able to print in list format using below:

    for i in range(1,5):
        print [j for j in range(1,i+1) ], [j for j in range(i-1,0,-1) ]

Result:

[1] []
[1, 2] [1]
[1, 2, 3] [2, 1]
[1, 2, 3, 4] [3, 2, 1]
[1, 2, 3, 4, 5] [4, 3, 2, 1]

edited Dec 26 '20 at 14:37

Red

26,798
7
36
58

answered Sep 26 '17 at 16:12

Vaibhav jain

31
2

score 0 · Answer 11 · edited Jul 13 '19 at 09:54

0

I think the following code should work. I have used the most basic method, so that most people are going to understand it:

  N = int(input())
  arr = []
  for i in range(1,N+1):
         arr.append(i)
         print(arr+arr[-2: :-1])

edited Jul 13 '19 at 09:54

double-beep

5,031
17
33
41

answered Jul 13 '19 at 07:18

Taalib Zama

89
3

score 0 · Answer 12 · answered Jun 13 '22 at 13:21

0

I know this has been asked a while ago, but I just stumbled upon this exercise and found an alternative and elegant solution to it.

As suggested by @raina77ow, we know that 11 * 11 = 121, 111 * 111 = 12321 and so on. But we also know that:

2**1 - 1 = 1 (is 1 in binary)
2**2 - 1 = 3 (is 11 in binary)
2**3 - 1 = 7 (is 111 in binary)
2**4 - 1 = 15 (is 1111 in binary)
etc.

Now, by doing bin(15) you get 0b1111 and I hate that I had to transform it to integer using slicing, but I found no other method.

So, using the above, this is my solution:

for i in range(1,int(input())+1):  # given line
    print(int(bin(2**i - 1)[2:])**2)

answered Jun 13 '22 at 13:21

Leonte Andrei

11

This is an interesting alternative solution. I'm not sure why it was voted down, but it might be less efficient because of the conversion and array. You'd have to run timing tests to see. – bikemule Apr 16 '23 at 09:56
@bikemule all tests passed on their website. I guess stricter test cases could show a difference. Thanks for your evaluation! – Leonte Andrei Apr 17 '23 at 14:02

score -1 · Answer 13 · answered Jun 17 '18 at 10:08

    for i in range(2,int(raw_input())+2): 
        print ''.join(([unicode(k) for k in range(1,i)]))+""+''.join(([unicode(k) for k in range(i-2,0,-1)]))
        print ''.join(map(unicode,range(1,i)))+""+''.join(map(unicode,range(i-2,0,-1)))

I hope it will help.

score -1 · Answer 14 · edited Aug 13 '19 at 06:50

-1

Use this code:

prefix = ''
suffix = ''

for i in range(1,n):
    middle = str(i)
    string = prefix + middle + suffix
    print(string)

    prefix = prefix + str(i)
    suffix = ''.join(reversed(prefix))

edited Aug 13 '19 at 06:50

jkdev

11,360
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54
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answered Aug 13 '19 at 04:40

Anmol Parida

672
5
16

@jkdev what was wrong with my code, why the down vote – Anmol Parida Aug 13 '19 at 08:31
I only added “Use this code:” before the code block. No edits to the code block itself. – jkdev Aug 13 '19 at 08:35

DuckyShine · Answer 15 · 2020-05-02T12:32:14.230

for i in range(1,int(input())+1):
    print(int(str('1'*i))**2)

Basically on each iteration, the number '1' in string is multiplied by i times then converted to an integer then squared. So e.g.

On the 3rd iteration --> output = 111^2 = 12321

Edit: Noticed constraints was to answer with str() function

So we have a sequence 1, 11, 111, 1111 nth = an + (a(r^(n-1) - 1)) / (r - 1) where |r > 1|

therefore, solution;

for i in range(1,int(input())+1):
    print(pow((((10**i - 10))//9) + 1, 2))

dw00600 · Answer 16 · 2022-11-03T20:38:21.530

-1

Putting in my two cents worth, using unpacking of range

    for i in range(1, int(input()) + 1):
        print (*range(1, i+1), *range(i-1, 0, -1))

Just noticed Keith Hall has a very similar solution. He should get original credit for this.

edited Nov 03 '22 at 20:38

answered Nov 03 '22 at 20:27

dw00600

1
1
2

score -1 · Answer 17 · answered Dec 25 '22 at 15:00

-1

Easy Way for this

if __name__ == '__main__':
n = int(input())
st = ''
st2 = ''
for i in range(1,n+1):
    st += str(i)
    if i==0:
        print(st)
    else:
        st2 = str(i-1) + st2
        print(st+st2.rstrip('0'))

answered Dec 25 '22 at 15:00

Jyotisha Chaurasia

1
1

As it’s currently written, your answer is unclear. Please [edit] to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers [in the help center](/help/how-to-answer). – Community Dec 26 '22 at 02:12
Users find it difficult to understand code only answers with no explanation. Please consider adding some description explaining how it solves the problem or add comments in the source code at appropriate places. – Azhar Khan Dec 26 '22 at 14:11

Solving palindromic 'Triangle Quest' puzzle in Python

17 Answers17