%!PS

% begin included library code
% see https://codeberg.org/Firedrake/postscript-libraries/
/test {
    /test.count test.count 1 add def
    {
        /test.pass test.pass 1 add def
    } {
        ( ) print
        test.count (....) cvs print
        (-fail) print
    } ifelse
} bind def

/test.start {
    print (:) print
    /test.pass 0 def
    /test.count 0 def
} bind def

/combinations {
    4 dict begin
    /k exch def
    /arr exch def
    /c [
        0 1 k 1 sub { } for
        arr length
        0
    ] def
    [
        {
            [
                k 1 sub -1 0 {
                    c exch get arr exch get
                } for
            ]
            /j 0 def
            {
                c j get 1 add c j 1 add get ne {
                    exit
                } if
                c j j put
                /j j 1 add def
            } loop
            j k ge {
                exit
            } if
            c j c j get 1 add put
        } loop
    ]
    end
} bind def

/map { % array proc -> array
    2 dict begin
    /p exch def
    [ exch
      {
          p
      } forall
    ]
    end
} bind def

/reduce { % array proc -> value
    2 dict begin
    /p exch def
    /a exch def
    a 0 get
    1 1 a length 1 sub {
        a exch get
        p
    } for
    end
} bind def

/permute { % [array] {proc} permute runs proc on each permutation of array
    7 dict begin
    /permute.subproc exch def
    /permute.a exch def
    /permute.n permute.a length def
    /permute.c [ permute.n { 0 } repeat ] def
    permute.a permute.subproc
    /permute.i 0 def
    {
        permute.i permute.n ge {
            exit
        } if
        permute.c permute.i get permute.i lt {
            permute.i 2 mod 0 eq {
                0 permute.i permute.swap
            } {
                permute.c permute.i get permute.i permute.swap
            } ifelse
            permute.a permute.subproc
            permute.c permute.i get 1 add permute.c exch permute.i exch put
            /permute.i 0 def
        } {
            permute.c permute.i 0 put
            /permute.i permute.i 1 add def
        } ifelse
    } loop
    end
} bind def

/test.end {
    ( ) print
    test.count 0 gt {
        (Passed ) print
        test.pass (...) cvs print
        (/) print
        test.count (...) cvs print
        ( \() print
        test.pass 100 mul test.count idiv (...) cvs print
        (%\)) print
        (\r\n) print
    } if
} bind def

/filter { % array proc(bool) -> array
    1 dict begin
    /p exch def
    [ exch
      {
          dup p not
          {
              pop
          } if
      } forall
    ]
    end
} bind def

/permute.swap {
    /permute.bi exch def
    /permute.ai exch def
    permute.a permute.ai get
    permute.a permute.bi get
    permute.a exch permute.ai exch put
    permute.a exch permute.bi exch put
} bind def

/toset { % array -> dict of (value, true)
    << exch
       {
           true
       } forall
    >>
} bind def

/listmax {
    { max } reduce
} bind def


% end included library code

/arraypairing {
    9 dict begin
    /n exch def
    /nl n length def
    nl 2 mod 1 eq {
        0
    } {
        /hl nl 2 idiv def
        [
            [ 0 1 nl 1 sub {} for ]
            hl
            combinations {
                /px exch def
                /pa [
                    px {
                        n exch get
                    } forall
                ] def
                /ps px toset def
                /pb [ 0 1 nl 1 sub {} for ]
                { ps exch known not } filter
                { n exch get } map def
                pa {
                    /pp exch def
                    /s 0 def
                    0 1 hl 1 sub {
                        /i exch def
                        /s pp i get pb i get min s add def
                    } for
                    s
                } permute
            } forall
        ] listmax
    } ifelse
    end
} bind def

(arraypairing) test.start
[1 2 3 4] arraypairing 4 eq test
[0 2 1 3] arraypairing 2 eq test
test.end