# Euler problems/81 to 90

### From HaskellWiki

m (Corrected the links to Project Euler) |
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Solution: |
Solution: |
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<haskell> |
<haskell> |
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− | problem_87 = undefined |
+ | import List |

+ | |||

+ | problem_87 = length expressible |
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+ | where limit = 50000000 |
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+ | squares = takeWhile (<limit) (map (^2) primes) |
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+ | cubes = takeWhile (<limit) (map (^3) primes) |
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+ | fourths = takeWhile (<limit) (map (^4) primes) |
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+ | choices = [[s,c,f] | s <- squares, c <- cubes, f <- fourths] |
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+ | unique = map head . group . sort |
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+ | expressible = filter (<limit) . unique . map sum $ choices |
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</haskell> |
</haskell> |
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## Revision as of 22:54, 15 August 2007

## Contents |

## 1 Problem 81

Find the minimal path sum from the top left to the bottom right by moving right and down.

Solution:

problem_81 = undefined

## 2 Problem 82

Find the minimal path sum from the left column to the right column.

Solution:

problem_82 = undefined

## 3 Problem 83

Find the minimal path sum from the top left to the bottom right by moving left, right, up, and down.

Solution:

problem_83 = undefined

## 4 Problem 84

In the game, Monopoly, find the three most popular squares when using two 4-sided dice.

Solution:

problem_84 = undefined

## 5 Problem 85

Investigating the number of rectangles in a rectangular grid.

Solution:

problem_85 = undefined

## 6 Problem 86

Exploring the shortest path from one corner of a cuboid to another.

Solution:

problem_86 = undefined

## 7 Problem 87

Investigating numbers that can be expressed as the sum of a prime square, cube, and fourth power?

Solution:

import List problem_87 = length expressible where limit = 50000000 squares = takeWhile (<limit) (map (^2) primes) cubes = takeWhile (<limit) (map (^3) primes) fourths = takeWhile (<limit) (map (^4) primes) choices = [[s,c,f] | s <- squares, c <- cubes, f <- fourths] unique = map head . group . sort expressible = filter (<limit) . unique . map sum $ choices

## 8 Problem 88

Exploring minimal product-sum numbers for sets of different sizes.

Solution:

problem_88 = undefined

## 9 Problem 89

Develop a method to express Roman numerals in minimal form.

Solution:

problem_89 = undefined

## 10 Problem 90

An unexpected way of using two cubes to make a square.

Solution:

problem_90 = undefined