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

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

## Revision as of 14:58, 30 August 2007

## Contents

## Problem 91

Find the number of right angle triangles in the quadrant.

Solution:

```
problem_91 = undefined
```

## Problem 92

Investigating a square digits number chain with a surprising property.

Solution:

```
problem_92 = undefined
```

## Problem 93

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

Solution:

```
problem_93 = undefined
```

## Problem 94

Investigating almost equilateral triangles with integral sides and area.

Solution:

```
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.

Solution:

```
problem_96 = undefined
```

## Problem 97

Find the last ten digits of the non-Mersenne prime: 28433 × 2^{7830457} + 1.

Solution:

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

## Problem 98

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

Solution:

```
problem_98 = undefined
```

## Problem 99

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

Solution:

```
problem_99 = undefined
```

## Problem 100

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

Solution:

```
problem_100 = undefined
```