day2.md

Challenge 2 (11/04/2020)

Given a list of elements, a surpasser of an element is an element on its right hand side that is larger than it. The surpasser count of an element is the number of its surpassers. Return the maximum surpasser count of a list.

Premises

• List of elements may occupy max memory size;
• The set of elements are any a poset (orderable);

Examples

msc of G,E,N,E,R,A,T,I,N,G is 6
msc of 10,3,4,5,2 is 2

Solutions

(18) APL by Hugo

msc←{⌈/+/¨⍵<⊖,\⊖⍵}

(42) APL by Hugo

msc←{1>⍴⍵:0⋄H←(1↑⍵)⋄(+/{H<⍵}¨(1↓⍵))⌈∇(1↓⍵)}

(42) Haskell by Restivo

msc[]=0;msc(h:t)=sum[1|y<-t,y>h]`max`msc t

(43) Haskell by André Silva

msc[]=0;msc(h:t)=max(sum[1|x<-t,h<x])$msc t

(43) Haskell by Hugo

msc l=maximum[sum[1|x<-t,x>h]|h:t<-tails l]

(50) Haskell by Hugo

msc=maximum.ap(zipWith((length.).filter.(<)))tails

(57) Julia by Ferrolho

msc(x)=maximum(count(>(x[i]),x[i:end]) for i=1:length(x))

(73) Python by António

msc=lambda l: max([sorted(l[i:])[::-1].index(e) for i,e in enumerate(l)])

(76) Python by Mafalda

msc=lambda l:max([len([x for x in l[e:] if x>l[e]]) for e in range(len(l))])

(79) Haskell by Mafalda

msc l=maximum(map length(groupBy(==)[x|x<-[0..length l-1],y<-drop x l,y>l!!x]))

(100 😢) Swift by Tiago

func msc<T:Comparable>(_ l:[T]){l.enumerated().map{i,e in l.dropFirst(i).filter{e<$0}.count}.max()!}

Either by ignorance or by Swift type system, in order to work with Array of Arrays we need to teach Swift how we want to compare those arrays.

extension Array: Comparable where Element: Comparable {
    public static func < (lhs: [Element], rhs: [Element]) -> Bool {
        return lhs.count < rhs.count
    }
}