Difference between revisions of "Euler problems/171 to 180"
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== [http://projecteuler.net/index.php?section=problems&id=174 Problem 174] == |
== [http://projecteuler.net/index.php?section=problems&id=174 Problem 174] == |
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Counting the number of "hollow" square laminae that can form one, two, three, ... distinct arrangements. |
Counting the number of "hollow" square laminae that can form one, two, three, ... distinct arrangements. |
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− | Solution: This was my C++ code, published here without my permission nor any attribution, shame on whoever put it here. [[user:henk263|henk263]] |
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== [http://projecteuler.net/index.php?section=problems&id=175 Problem 175] == |
== [http://projecteuler.net/index.php?section=problems&id=175 Problem 175] == |
Revision as of 08:42, 26 February 2008
Problem 171
Finding numbers for which the sum of the squares of the digits is a square.
Solution: this was Antoine Celeriers C code pasted from the Project Euler Forum.
Problem 172
Investigating numbers with few repeated digits.
Solution:
factorial n = product [1..toInteger n]
fallingFactorial x n = product [x - fromInteger i | i <- [0..toInteger n - 1] ]
choose n k = fallingFactorial n k `div` factorial k
-- how many numbers can we get having d digits and p positions
p172 0 _ = 0
p172 d p
| p < 4 = d^p
| otherwise =
(p172' p) + p*(p172' (p-1)) + (choose p 2)*(p172' (p-2)) + (choose p 3)*(p172' (p-3))
where
p172' = p172 (d-1)
problem_172= (p172 10 18) * 9 `div` 10
Problem 173
Using up to one million tiles how many different "hollow" square laminae can be formed? Solution:
problem_173=
let c=div (10^6) 4
xm=floor$sqrt $fromIntegral c
k=[div c x|x<-[1..xm]]
in sum k-(div (xm*(xm+1)) 2)
Problem 174
Counting the number of "hollow" square laminae that can form one, two, three, ... distinct arrangements.
Problem 175
Fractions involving the number of different ways a number can be expressed as a sum of powers of 2. Solution:
sternTree x 0=[]
sternTree x y=
m:sternTree y n
where
(m,n)=divMod x y
findRat x y
|odd l=take (l-1) k++[last k-1,1]
|otherwise=k
where
k=sternTree x y
l=length k
p175 x y=
init$foldl (++) "" [a++","|
a<-map show $reverse $filter (/=0)$findRat x y]
problems_175=p175 123456789 987654321
test=p175 13 17
Problem 176
Rectangular triangles that share a cathetus. Solution:
--k=47547
--2*k+1=95095 = 5*7*11*13*19
lst=[5,7,11,13,19]
primes=[2,3,5,7,11]
problem_176 =
product[a^b|(a,b)<-zip primes (reverse n)]
where
la=div (last lst+1) 2
m=map (\x->div x 2)$init lst
n=m++[la]
Problem 177
Integer angled Quadrilaterals.
Solution: This C++ solution is stolen from balakrishnan. Check out the forum if you want to see his solution to the problem
Problem 178
Step Numbers
Count pandigital step numbers.
import qualified Data.Map as M
data StepState a = StepState { minDigit :: a
, maxDigit :: a
, lastDigit :: a
} deriving (Show, Eq, Ord)
isSolution (StepState i a _) = i == 0 && a == 9
neighborStates m s@(StepState i a n) = map (\x -> (x, M.findWithDefault 0 s m)) $
[StepState (min i (n - 1)) a (n - 1), StepState i (max a (n + 1)) (n + 1)]
allStates = [StepState i a n | (i, a) <- range ((0, 0), (9, 9)), n <- range (i, a)]
initialState = M.fromDistinctAscList [(StepState i i i, 1) | i <- [1..9]]
stepState m = M.fromListWith (+) $ allStates >>= neighborStates m
numSolutionsInMap = sum . map snd . filter (isSolution . fst) . M.toList
numSolutionsOfSize n = sum . map numSolutionsInMap . take n $ iterate stepState initialState
problem_178 = numSolutionsOfSize 40
Problem 179
Consecutive positive divisors.
Problem 180
Rational zeros of a function of three variables. Solution:
import Data.Ratio
{-
After some algebra, we find:
f1 n x y z = x^(n+1) + y^(n+1) - z^(n+1)
f2 n x y z = (x*y + y*z + z*x) * ( x^(n-1) + y^(n-1) - z^(n-1) )
f3 n x y z = x*y*z*( x^(n-2) + y^(n-2) - z^(n-2) )
f n x y z = f1 n x y z + f2 n x y z - f3 n x y z
f n x y z = (x+y+z) * (x^n+y^n-z^n)
Now the hard part comes in realizing that n can be negative.
Thanks to Fermat, we only need examine the cases n = [-2, -1, 1, 2]
Which leads to:
f(-2) z = xy/sqrt(x^2 + y^2)
f(-1) z = xy/(x+y)
f(1) z = x+y
f(2) z = sqrt(x^2 + y^2)
-}
unique :: Eq(a) => [a] -> [a]
unique [] = []
unique (x:xs) | elem x xs = unique xs
| otherwise = x : unique xs
-- Not quite correct, but I don't care about the zeros
ratSqrt :: Rational -> Rational
ratSqrt x =
let a = floor $ sqrt $ fromIntegral $ numerator x
b = floor $ sqrt $ fromIntegral $ denominator x
c = (a%b) * (a%b)
in if x == c then (a%b) else 0
-- Not quite correct, but I don't care about the zeros
reciprocal :: Rational -> Rational
reciprocal x
| x == 0 = 0
| otherwise = denominator x % numerator x
problem_180 =
let order = 35
range :: [Rational]
range = unique [ (a%b) | b <- [1..order], a <- [1..(b-1)] ]
fm2,fm1,f1,f2 :: [[Rational]]
fm2 = [[x,y,z] | x<-range, y<-range,
let z = x*y * reciprocal (ratSqrt(x*x+y*y)), elem z range]
fm1 = [[x,y,z] | x<-range, y<-range,
let z = x*y * reciprocal (x+y), elem z range]
f1 = [[x,y,z] | x<-range, y<-range,
let z = (x+y), elem z range]
f2 = [[x,y,z] | x<-range, y<-range,
let z = ratSqrt(x*x+y*y), elem z range]
result = sum $ unique $ map (\x -> sum x) (fm2++fm1++f1++f2)
in (numerator result + denominator result)