Problem Statement

Shuffle the characters of a string in such a way that as many of the character values are in a different position as possible. A shuffle that produces a randomized result among the best choices is to be preferred. A deterministic approach that produces the same sequence every time is acceptable as an alternative. Display the result as follows: The score gives the number of positions whose character value did not change.

Let's start with the solution:

bestShuf =: verb define
  yy=. <@({~ ?~@#)@I.@= y
  y C.~ (;yy) </.~ (i.#y) |~ >./#@> yy
)

fmtBest=:3 :0
  b=. bestShuf y
  y,', ',b,' (',')',~":+/b=y
)


   fmtBest&>;:'abracadabra seesaw elk grrrrrr up a'
abracadabra, bdacararaab (0)
seesaw, eawess (0)          
elk, lke (0)                
grrrrrr, rrrrrrg (5)        
up, pu (0)                  
a, a (1)