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Today's Topics:
1. Re: CSES programming problems at https://cses.fi/problemset/
(Irfon-Kim Ahmad)
2. Re: CSES programming problems at https://cses.fi/problemset/
(Julian Ong)
3. Re: CSES programming problems at https://cses.fi/problemset/
(Julian Ong)
----------------------------------------------------------------------
Message: 1
Date: Sun, 28 Jun 2020 12:48:12 -0400
From: Irfon-Kim Ahmad <ir...@ambienautica.com>
To: beginners@haskell.org
Subject: Re: [Haskell-beginners] CSES programming problems at
https://cses.fi/problemset/
Message-ID: <0bcd69e9-10d4-3f41-274f-8e860692a...@ambienautica.com>
Content-Type: text/plain; charset="utf-8"; Format="flowed"
On 2020-06-28 11:26 a.m., Doug McIlroy wrote:
>> I'm currently stuck on the Two Knights problem.
> Having placed one knight on the board, in how many
> places can you put the other?
If you check the website indicated, it's a slight variation on that:
"Your task is to count for k=1,2,…,nthe number of ways two knights can
be placed on a k×kchessboard so that they do not attack each other."
The input is n (an integer that can range from 1 to 10000), the output
is a single integer for each value from 1 to n, one per line, the memory
limit is 512MB, and the maximum runtime is 1.00 seconds.
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Message: 2
Date: Sun, 28 Jun 2020 23:27:07 +0000 (UTC)
From: Julian Ong <julian_...@yahoo.com>
To: beginners@haskell.org
Subject: Re: [Haskell-beginners] CSES programming problems at
https://cses.fi/problemset/
Message-ID: <1817199903.471182.1593386827...@mail.yahoo.com>
Content-Type: text/plain; charset="utf-8"
I realized I did not answer the question Doug posed, but the algorithm as
originally presented works correctly and calculates correctly the number of
possible knight pairings for each k x k board and generates the correct output
requested by the problem.
The issue is still that, as I have implemented it in Haskell, it doesn't run
fast enough to pass the automated CSES testing for n=10000. I am very curious
whether it's possible to pass the speed testing for this problem using Haskell
and if so how.
On Sunday, June 28, 2020, 09:49:02 AM PDT, Irfon-Kim Ahmad
<ir...@ambienautica.com> wrote:
On 2020-06-28 11:26 a.m., Doug McIlroy wrote:
I'm currently stuck on the Two Knights problem.
Having placed one knight on the board, in how many
places can you put the other?
If you check the website indicated, it's a slight variation on that:
"Your task is to count for k=1,2,…,n the number of ways two knights can be
placed on a k×k chessboard so that they do not attack each other."
The input is n (an integer that can range from 1 to 10000), the output is a
single integer for each value from 1 to n, one per line, the memory limit is
512MB, and the maximum runtime is 1.00 seconds.
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Message: 3
Date: Sun, 28 Jun 2020 23:45:18 +0000 (UTC)
From: Julian Ong <julian_...@yahoo.com>
To: beginners@haskell.org
Subject: Re: [Haskell-beginners] CSES programming problems at
https://cses.fi/problemset/
Message-ID: <1581505561.464885.1593387918...@mail.yahoo.com>
Content-Type: text/plain; charset="utf-8"
I've simplified and optimized it slightly (no need to use a monad for
moveKnightUR) but overall it's still not fast enough to pass the CSES test. I'm
wondering if the recursion is somehow inefficient because of two instances of
solveK (k-1)...?---- main :: IO ()main = do line <- getLine let n = read
line :: Integer putStr $ unlines $ map show $ reverse $ solveK n
solveK :: Integer -> [Integer]solveK k | k == 1 = [0] | otherwise =
(solveFrameK k + head (solveK (k-1))) : solveK (k-1)
-- Returns list of knight moves in the upper right (k-1) x (k-1) portion of the
board excluding the first column and first rowmoveKnightUR :: Integer ->
(Integer, Integer) -> [(Integer, Integer)]moveKnightUR k (c, r) = filter (\(c',
r') -> c' `elem` [2..k] && r' `elem` [2..k]) [(c-1, r+2), (c+1, r+2), (c+2,
r+1), (c+2, r-1), (c+1, r-2), (c-2, r+1)] -- Returns list of left and bottom
border squares for k x k board in (col, row) format with (1, 1) being the lower
left squaregenBorder :: Integer -> [(Integer, Integer)]genBorder k = [(1, a) |
a <- [1..k]] ++ [(a, 1) | a <- [2..k]]
-- Formula for combinations C(n, r)combinations :: Integer -> Integer ->
Integercombinations n r = product [1..n] `div` (product [1..(n-r)] * product
[1..r])
-- Calculates additional number of two knight placements along the left and
bottom border and from that border into the upper right (k-1) x (k-1)
regionsolveFrameK :: Integer -> IntegersolveFrameK k | k == 1 = 0 | k ==
2 = 6 | otherwise = ((combinations (2*k-1) 2) - 2) + (k-1) * (k-1) * (2*k-1)
- sum (map (toInteger . length) (map (moveKnightUR k) (genBorder k)))----
Julian
On Sunday, June 28, 2020, 04:27:07 PM PDT, Julian Ong
<julian_...@yahoo.com> wrote:
I realized I did not answer the question Doug posed, but the algorithm as
originally presented works correctly and calculates correctly the number of
possible knight pairings for each k x k board and generates the correct output
requested by the problem.
The issue is still that, as I have implemented it in Haskell, it doesn't run
fast enough to pass the automated CSES testing for n=10000. I am very curious
whether it's possible to pass the speed testing for this problem using Haskell
and if so how.
On Sunday, June 28, 2020, 09:49:02 AM PDT, Irfon-Kim Ahmad
<ir...@ambienautica.com> wrote:
On 2020-06-28 11:26 a.m., Doug McIlroy wrote:
I'm currently stuck on the Two Knights problem.
Having placed one knight on the board, in how many
places can you put the other?
If you check the website indicated, it's a slight variation on that:
"Your task is to count for k=1,2,…,n the number of ways two knights can be
placed on a k×k chessboard so that they do not attack each other."
The input is n (an integer that can range from 1 to 10000), the output is a
single integer for each value from 1 to n, one per line, the memory limit is
512MB, and the maximum runtime is 1.00 seconds.
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Beginners mailing list
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