eight queens puzzle
8 queens problem
8 queens puzzle
eight queens problem

    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.

   [Best algorithm?]

   (1999-07-28)