I have a few more issues with my n queens program but I have been making
progress :)
First On an 8x8 board The program can discover what the missing elements
are, but for some reason does not add the final element to the list, which
it should then return.
Secondly I have a limit on the expected size of the board the upper limit is
16x16 board but when I enter 16 in the board selection dialog box, the
n-queens algorithm will only run to a maximum of 12 queens, I do not know if
this is linked to my first problem.
Further testing shows on an 8x8 grid with 7 of the queens provided the
program cant find the final element, yet increase the board size to 16 (and
although it will only run to 12) you will get the 8th queen position. Below
are my functions if anyone could help me work out where my last few issues
are, I would be grateful.
fun {Queens L N}
if {GetLengthOfList L} == N then
{Browse L}
L
else
{Browse L}
{Queens {Revise 0|L} N}
end
end
fun {GetLengthOfList L}
case L of H|T then
1+{GetLengthOfList T}
else
0
end
end
fun {Revise L}
case L of H|T then
if H == BoardSize then {Revise T}
else N = {GetLengthOfList L} in
if {Threaten {BuildList T} H+1#N} then {Revise H+1|T}
else {AddToList H+1#N T}
end
end
else nil
end
end
fun {BuildList L}
case L of H|T then
%{Browse H.1#{GetLengthOfList L}}
H.1#{GetLengthOfList L}|{BuildList T}
else
nil
end
end
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