--  eight-queens
--  Author: Hannes du Plooy 
--  Date: 20 Sep 2016      
--  Objective: To solve the following
--  Search for a chess board solution with 8 queens and no one
--  endangering any other.
board = {0,0,0,0,0,0,0,0}

function EightQueens(line)
    if line>7 then return true end
    for column = 0,7 do
        endangered = false
        for line2 = 0,line-1 do
            if board[line2]==column or math.abs(line-line2)==math.abs(column-board[line2]) then
                endangered = true
                break
            end
        end
        if not endangered then
            board[line] = column
            if EightQueens(line+1) then
                return true
            end
        end
    end
    return false
end

if EightQueens(0) then
    for i=0,7 do
        tmp = ""
        for j=0,7 do
            if board[i] == j then
                tmp = tmp .. "Q"
            else
                tmp = tmp .. "."
            end
        end
        print(tmp)
    end
end