combinations clear solution for The Longest Palindromic by gyahun_dash - python coding challenges

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combinations solution in Clear category for The Longest Palindromic by gyahun_dash

from itertools import combinations as C

def longest_palindromic(text):
    subs = (text[start: end] for start, end in C(range(len(text) + 1), 2))
    return max((s for s in subs if s == s[::-1]), key=len)

March 2, 2016

Comments:

IWyf on Aug. 23, 2016, 4:27 a.m.
This is very python

Hayertjez on Sept. 30, 2016, 1:45 p.m.
Why a sub sequence length of 2? <pre class='brush: python'>C(range(len(text) + 1), 2) </pre> Short solution.

gyahun_dash on Oct. 4, 2016, 2:23 p.m.
It generates left and right indices of text: <pre class='brush: python'>C(range(len('spam') + 1), 2) -> 0, 1: 's' -> 0, 2: 'sp' -> 0, 3: 'spa' -> 0, 4: 'spam' -> 1, 2: 'p' ... </pre>

vovoka on Oct. 30, 2018, 4:05 p.m.
Elegant solution (not sure about it's effectiveness, but it's short and cool.) However, I've stuck trying to learn this trick. In <a href="https://docs.python.org/3/library/itertools.html#itertools.combinations">docs.python</a> written next: <pre class='brush: python'>itertools.combinations(iterable, r) Return r length subsequences of elements from the input iterable. ... def combinations(iterable, r): # combinations('ABCD', 2) --> AB AC AD BC BD CD # combinations(range(4), 3) --> 012 013 023 123 ... </pre> In your code r = 2. So I expect your code checked only 2-chars-strings. However, it's worked as you wrote above. 0_о Сould you explain one more time, why in combinations(iterable, r) your r-value = 2? What I missed? Thank you in advance!

vovoka on Oct. 31, 2018, 6:01 a.m.
At morning I got it. r=2 because in your case it's a combination of indices(and 'r' are start and end indices). Solved)

prlombaard on Oct. 7, 2016, 8:13 p.m.
Wow, amazing, must agree with @IWyf this is very Pythonic. Although I must also say it does take some time to read and dissect and understand what exactly the code does. But very cleverly done! @gyahun_dash was this your first solution to this mission?

grackhack on Feb. 3, 2017, 2:51 p.m.
Одним словом хрен поймешь сразу. )))

viktor.chyrkin on Jan. 29, 2022, 12:57 a.m.
я не единствиный кто говорит по русски!

iir_72294cbb98dc4ee1b66645f0bf on Aug. 8, 2017, 10:42 a.m.
Why not? =))) from itertools import combinations as C longest_palindromic = lambda data: max((s for s in (data[s: e] for s, e in C(range(len(data) + 1), 2)) if s == s[::-1]), key=len)

martin.pilka on Jan. 26, 2019, 9:28 p.m.
I believe this solution does not meet `Try to be as efficient as possible!` part of problem description.

eugene100372 on May 14, 2019, 9:16 a.m.
short and pythonic solution, incommensurably better than my unpublished, But! its computational complexity O(n^3) is even worse than a sufficiently straightforward algorithm with O(n^2). This classical problem has an optimal solution in linear time (the Manaсher algorithm) and methodologically interesting solutions with O(n*log(n)). The best of the really quick solutions on the site has 24 points, the rest are not included Top 30.

Venigret on Aug. 23, 2022, 1:09 p.m.
These is a long comment just to get quest I'm actually didn't like itertools but it is wery usefull in some tasks but I just want my 4 points

flowerinapot on June 9, 2023, 5:56 p.m.
It's genius and simple. Like it

U.V on Sept. 21, 2023, 2:10 p.m.
This is really pythonic solution

U.V on Nov. 22, 2024, 9:24 a.m.
Elegant using of itertools.combinations !

Strings Theory

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