%!PS

% begin included library code
% see https://codeberg.org/Firedrake/postscript-libraries/
/quicksort {
    { quicksort.cmp } quicksort.with_comparator
} 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

/quicksort.main { % lo hi -> (null)
    3 dict begin
    /hi exch def
    /lo exch def
    /xit false def
    lo 0 lt {
        /xit true def
    } if
    hi 0 lt {
        /xit true def
    } if
    lo hi ge {
        /xit true def
    } if
    xit not {
        /p quicksort.partition def
        lo p quicksort.main
        p 1 add hi quicksort.main
    } if
    end
} bind def

/listmin {
    { min } reduce
} bind def

/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

/quicksort.with_comparator { % [ a c b ] { comparator } -> [ a b c ]
    2 dict begin
    /cmp exch def
    /arr exch def
    arr length 0 gt {
        0 arr length 1 sub quicksort.main
    } if
    arr
    end
} bind def

/quicksort.swap {
    2 dict begin
    /bi exch def
    /ai exch def
    arr ai get
    arr bi get
    arr exch ai exch put
    arr exch bi exch put
    end
} bind def

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

/keys { % dict -> array of dict keys
    [ exch
      {
          pop
      } forall
    ]
} bind def

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

/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

/quicksort.cmp {
    2 copy
    lt {
        pop pop -1
    } {
        gt {
            1
        } {
            0
        } ifelse
    } ifelse
} bind def

/quicksort.partition {
    3 dict begin
    /pivot arr hi lo add 2 idiv get def
    /i lo 1 sub def
    /j hi 1 add def
    {
        {
            /i i 1 add def
            arr i get pivot cmp 0 ge {
                exit
            } if
        } loop
        {
            /j j 1 sub def
            arr j get pivot cmp 0 le {
                exit
            } if
        } loop
        i j ge {
            j
            exit
        } if
        i j quicksort.swap
    } loop
    end
} bind def

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


% end included library code

/strongpair {
    0 dict begin
    toset keys quicksort
    2 combinations {
        /c exch def
        c 0 get c 1 get sub abs c listmin lt
    } filter length
    end
} bind def

(strongpair) test.start
[1 2 3 4 5] strongpair 4 eq test
[5 7 1 7] strongpair 1 eq test
test.end