Euler problems/101 to 110
Revision as of 12:50, 9 December 2007
Investigate the optimum polynomial function to model the first k terms of a given sequence.
problem_101 = undefined
For how many triangles in the text file does the interior contain the origin?
import List split :: Char -> String -> [String] split = unfoldr . split' split' :: Char -> String -> Maybe (String, String) split' c l | null l = Nothing | otherwise = Just (h, drop 1 t) where (h, t) = span (/=c) l isOrig (x1:y1:x2:y2:x3:y3:)= t1*t2>=0 && t3*t4>=0 && t5*t6>=0 where x4=0 y4=0 t1=(y2-y1)*(x4-x1)+(x1-x2)*(y4-y1) t2=(y2-y1)*(x3-x1)+(x1-x2)*(y3-y1) t3=(y3-y1)*(x4-x1)+(x1-x3)*(y4-y1) t4=(y3-y1)*(x2-x1)+(x1-x3)*(y2-y1) t5=(y3-y2)*(x4-x2)+(x2-x3)*(y4-y2) t6=(y3-y2)*(x1-x2)+(x2-x3)*(y1-y2) sToInt x=map ((+0).read) $split ',' x problem_102=do x<-readFile "triangles.txt" print $length$ filter isOrig$map sToInt $lines x
Investigating sets with a special subset sum property.
problem_103 = undefined
Finding Fibonacci numbers for which the first and last nine digits are pandigital.
Very nice problem. I didnt realize you could deal with the precision problem. Therefore I used this identity to speed up the fibonacci calculation: f_(2*n+k) = f_k*(f_(n+1))^2 + 2*f_(k-1)*f_(n+1)*f_n + f_(k-2)*(f_n)^2
import Data.List import Data.Char fibos = rec 0 1 where rec a b = a:rec b (a+b) fibo_2nk n k = let fkm1 = fibo (k-1) fkm2 = fibo (k-2) fk = fkm1 + fkm2 fnp1 = fibo (n+1) fnp1sq = fnp1^2 fn = fibo n fnsq = fn^2 in fk*fnp1sq + 2*fkm1*fnp1*fn + fkm2*fnsq fibo x = let threshold = 30000 n = div x 3 k = n+mod x 3 in if x < threshold then fibos !! x else fibo_2nk n k findCandidates = rec 0 1 0 where m = 10^9 rec a b n = let continue = rec b (mod (a+b) m) (n+1) isBackPan a = (sort $ show a) == "123456789" in if isBackPan a then n:continue else continue search = let isFrontPan x = (sort $ take 9 $ show x) == "123456789" in map fst $ take 1 $ dropWhile (not.snd) $ zip findCandidates $ map (isFrontPan.fibo) findCandidates problem_104 = search
It took 8 sec on a 2.2Ghz machine.
The lesson I learned fom this challenge, is: know mathematical identities and exploit them. They allow you take short cuts. Normally you compute all previous fibonacci numbers to compute a random fibonacci number. Which has linear costs. The aforementioned identity builds the number not from its two predecessors but from 4 much smaller ones. This makes the algorithm logarithmic in its complexity. It really shines if you want to compute a random very large fibonacci number. f.i. the 10mio.th fibonacci number which is over 2mio characters long, took 20sec to compute on my 2.2ghz laptop.
Find the sum of the special sum sets in the file.
problem_105 = undefined
Find the minimum number of comparisons needed to identify special sum sets.
problem_106 = undefined
Determining the most efficient way to connect the network.
problem_107 = undefined
Solving the Diophantine equation 1/x + 1/y = 1/n.
import List primes=[2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73] series _ 1 =[] series xs n =[x:ps|x<-xs,ps<-series [0..x] (n-1) ] distinct=product. map (+1) sumpri x=product $map (\(x,y)->x^y)$zip primes x prob x y =head$sort[(sumpri m ,m)|m<-series [1..3] x,(>y)$distinct$map (*2) m] problem_108=prob 7 2000
How many distinct ways can a player checkout in the game of darts with a score of less than 100?
problem_109 = undefined
10 Problem 110
Find an efficient algorithm to analyse the number of solutions of the equation 1/x + 1/y = 1/n.
-- prob in problem_108 problem_110 = prob 13 (8*10^6)