99 problems in Julia (11-20)

In this article i am proudly presenting solutions to 11-20 problems from classical 99 Haskell problem set.

 Problem 11

Modify the result of problem 10 in such a way that if an element has no duplicates it is simply copied into the result list. Only elements with duplicates are transferred as (N E) lists.
Example:
Haskell Example:

* (encode-modified '(a a a a b c c a a d e e e e))
((4 A) B (2 C) (2 A) D (4 E))

Solution:
julia>function modifiedEncoding(x)
        lest=[]
        for c in unique(x)
                if counter(x,c)>1
                        lest=[lest...,(counter(x,c),c)]
                else
                        lest=[lest...,c]
                end
        end
   lest

end

julia>function counter(l,el)
        temp=0
        for i=1:endof(l)
                if el==l[i]
                        temp+=1
                end
        end
     temp
end

Problem 12

(**) Decode a run-length encoded list.
Given a run-length code list generated as specified in problem 11. Construct its uncompressed version.
Example in Haskell:

P12> decodeModified 
       [Multiple 4 'a',Single 'b',Multiple 2 'c',
        Multiple 2 'a',Single 'd',Multiple 4 'e']

Solution:
julia>function de_encode(x)
        lest=[]
        for c in x
                if typeof(c)==(Int32,Int32)
                        for i=1:c[1]
                                lest=[lest...,c[2]]
                        end
                else
                        lest=[lest...,c]
                end
        end
    lest
end

Problem 13

(**) Run-length encoding of a list (direct solution).
Implement the so-called run-length encoding data compression method directly. I.e. don't explicitly create the sublists containing the duplicates, as in problem 9, but only count them. As in problem P11, simplify the result list by replacing the singleton lists (1 X) by X.
Example:

* (encode-direct '(a a a a b c c a a d e e e e))
((4 A) B (2 C) (2 A) D (4 E))

Solution:

Same as problem 11.We used shortcut solution already in our early 11th problem.

Problem 14

(*) Duplicate the elements of a list.
Example:
* (dupli '(a b c c d))
(A A B B C C C C D D)

Solution:
julia>function duplicate(x)
        lest=[]
        for c in x
                lest=[lest...,c,c]
        end
    lest
end

Problem 15

(**) Replicate the elements of a list a given number of times.
Example:

* (repli '(a b c) 3)
(A A A B B B C C C) 

Solution: 

julia>function replicate(x,k)
        lest=[]
        for c in x
                for i=1:k
                        lest=[lest...,c]
                end
        end
    lest
end

 Problem 16

(**) Drop every N'th element from a list.
Example:
* (drop '(a b c d e f g h i k) 3) (A B D E G H K)
 Solution:
julia>function dropN(x,n)
        lest=[]
        for i=1:endof(x)
                if i%n!=0
                        lest=[lest...,x[i]]
                end
        end
    lest
end

Problem 17

(*) Split a list into two parts; the length of the first part is given.
Do not use any predefined predicates.
Example:

* (split '(a b c d e f g h i k) 3)
( (A B C) (D E F G H I K))

Solution: 

julia>split(x,n)=x[1:n],x[n+1,end]

Problem 18

(**) Extract a slice from a list.
Given two indices, i and k, the slice is the list containing the elements between the i'th and k'th element of the original list (both limits included). Start counting the elements with 1.
Example:
* (slice '(a b c d e f g h i k) 3 7)
   (C D E F G)

Solution:
julia>slice(x,i,j)=x[i:j]

Problem 19

(**) Rotate a list N places to the left.
Hint: Use the predefined functions length and (++).
Examples:

* (rotate '(a b c d e f g h) 3)
(D E F G H A B C)

* (rotate '(a b c d e f g h) -2)
(G H A B C D E F)

Solution: 

 julia>rotLeft(x,n)=[x[n+1:end],x[1:n]]

Problem 20

(*) Remove the K'th element from a list.
Example in Prolog:

?- remove_at(X,[a,b,c,d],2,R).
X = b
R = [a,c,d]

Solution: 

julia>removeAt(x,n)=delete!(x,n)

This delete!() method will go to jail because it changes original list which 

is anti philosophy of functional programming.Here is functional version.

julia>function removeAt(x,n)
        lest=[]
        for i=1:endof(x)
                if i!=n
                        lest=[lest...,x[i]]
                end
        end
   lest
end

Thanks for your patience.see you next time.