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98 lines
2.1 KiB
98 lines
2.1 KiB
-- Test file for Kate's Euphoria syntax highlighting/code folding.
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-- BEGIN region marker test
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-- code here
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-- END region marker test
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-- The N Queens Problem:
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-- Place N Queens on an NxN chess board
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-- such that they don't threaten each other.
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constant N = 8 -- try some other sizes
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constant ROW = 1, COLUMN = 2
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constant TRUE = 1, FALSE = 0
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type square(sequence x)
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-- a square on the board
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return length(x) = 2
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end type
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type row(integer x)
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-- a row on the board
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return x >= 1 and x <= N
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end type
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function threat(square q1, square q2)
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-- do two queens threaten each other?
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if q1[COLUMN] = q2[COLUMN] then
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return TRUE
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elsif q1[ROW] - q1[COLUMN] = q2[ROW] - q2[COLUMN] then
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return TRUE
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elsif q1[ROW] + q1[COLUMN] = q2[ROW] + q2[COLUMN] then
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return TRUE
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elsif q1[ROW] = q2[ROW] then
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return TRUE
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else
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return FALSE
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end if
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end function
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function conflict(square q, sequence queens)
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-- Would square p cause a conflict with other queens on board so far?
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for i = 1 to length(queens) do
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if threat(q, queens[i]) then
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return TRUE
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end if
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end for
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return FALSE
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end function
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integer soln
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soln = 0 -- solution number
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procedure print_board(sequence queens)
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-- print a solution, showing the Queens on the board
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integer k
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position(1, 1)
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printf(1, "Solution #%d\n\n ", soln)
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for c = 'a' to 'a' + N - 1 do
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printf(1, "%2s", c)
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end for
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puts(1, "\n")
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for r = 1 to N do
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printf(1, "%2d ", r)
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for c = 1 to N do
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if find({r,c}, queens) then
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puts(1, "Q ")
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else
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puts(1, ". ")
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end if
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end for
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puts(1, "\n")
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end for
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puts(1, "\nPress Enter. (q to quit) ")
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while TRUE do
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k = get_key()
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if k = 'q' then
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abort(0)
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elsif k != -1 then
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exit
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end if
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end while
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end procedure
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procedure place_queen(sequence queens)
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-- place queens on a NxN chess board
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-- (recursive procedure)
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row r -- only need to consider one row for each queen
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if length(queens) = N then
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soln += 1
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print_board(queens)
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return
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end if
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r = length(queens)+1
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for c = 1 to N do
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if not conflict({r,c}, queens) then
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place_queen(append(queens, {r,c}))
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end if
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end for
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end procedure
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