<algorithm> A puzzle in which one has to place eight queens on
a chessboard such that no queen is attacking any other,
i.e. no two queens occupy the same row, column or diagonal.
One may have to produce all possible such configurations or
just one.
It is a common students assignment to devise a program to
solve the eight queens puzzle. The brute force algorithm
tries all 64*63*62*61*60*59*58*57 = 178,462,987,637,760
possible layouts of eight pieces on a chessboard to see which
ones meet the criterion. More intelligent algorithms use the
fact that there are only ten positions for the first queen
that are not reflections of each other, and that the first
queen leaves at most 42 safe squares, giving only
10*42*41*40*39*38*37*36 = 1,359,707,731,200 layouts to try,
and so on.
The puzzle may be varied with different number of pieces and
different size boards.
