《Lua程序设计》-2.八皇后问题

N = 8;
function isplaceok(a,n,c)
    for i=1,n-1 do
        if a[i] == c or 
        (a[i] - c) == (i - n) or
        (a[i] - c) == (n - i)
        then
        return false;
            -- body
        end
    end
    return true;
end

function printSolution(a)
    for i=1,N do
        for j=1,N do
            io.write(a[i] == j and "X" or "-"," ");
        end
        io.write("\n");
    end
    io.write("\n");
end

function addQueen( a , n)
    getRes = false;
    if n > N then
        printSolution(a)
        getRes = true;
    else
        for c = 1, N do
            if  getRes == false and isplaceok(a,n,c) then
                a[n] = c;
                addQueen(a,n+1);
            end
        end

    end
end
addQueen({},1);