Difference between revisions of "Euler problems/91 to 100"

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(Solution for problem 94, not the best but still good (I think))
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import Data.Array.Unboxed
import Data.Array.Unboxed
import Prime
import qualified Data.IntSet as S
import qualified Data.IntSet as S
import Data.List
import Data.List

Revision as of 14:58, 30 August 2007

Problem 91

Find the number of right angle triangles in the quadrant.


problem_91 = undefined

Problem 92

Investigating a square digits number chain with a surprising property.


problem_92 = undefined

Problem 93

Using four distinct digits and the rules of arithmetic, find the longest sequence of target numbers.


problem_93 = undefined

Problem 94

Investigating almost equilateral triangles with integral sides and area.


problem_94 = undefined

Problem 95

Find the smallest member of the longest amicable chain with no element exceeding one million.

Solution which avoid visiting a number more than one time :

import Data.Array.Unboxed
import qualified Data.IntSet as S
import Data.List

chain n s =  lgo [n] $ properDivisorsSum ! n
    where lgo xs x | x > 1000000 || S.notMember x s = (xs,[])
                   | x `elem` xs = (xs,x : takeWhile (/= x) xs)
                   | otherwise = lgo (x:xs) $ properDivisorsSum ! x

properDivisorsSum :: UArray Int Int
properDivisorsSum = accumArray (+) 1 (0,1000000) 
                    $ (0,-1):[(k,factor)| 
                            factor<-[2..1000000 `div` 2]
                          , k<-[2*factor,2*factor+factor..1000000]

base = S.fromList [1..1000000]

problem_95 = fst $ until (S.null . snd) f ((0,0),base)
    where f ((n,m), s) = ((n',m'), s')
              where setMin = head $ S.toAscList s
                    (explored, chn) = chain setMin s
                    len = length chn
                    (n',m') = if len > m
                              then (minimum chn, len)
                              else (n,m)
                    s' = foldl' (flip S.delete) s explored

This solution need some space in its stack (it worked with 30M here).

Problem 96

Devise an algorithm for solving Su Doku puzzles.


problem_96 = undefined

Problem 97

Find the last ten digits of the non-Mersenne prime: 28433 × 27830457 + 1.


problem_97 = (28433 * 2^7830457 + 1) `mod` (10^10)

Problem 98

Investigating words, and their anagrams, which can represent square numbers.


problem_98 = undefined

Problem 99

Which base/exponent pair in the file has the greatest numerical value?


problem_99 = undefined

Problem 100

Finding the number of blue discs for which there is 50% chance of taking two blue.


problem_100 = undefined