Eight queens puzzle

abcdefgh
8
f8 white queen
d7 white queen
g6 white queen
a5 white queen
h4 white queen
b3 white queen
e2 white queen
c1 white queen
8
77
66
55
44
33
22
11
abcdefgh
The only symmetrical solution to the eight queens puzzle (up to rotation and reflection)

The eight queens puzzle is the problem of placing eight chess queens on an 8×8 chessboard so that no two queens threaten each other; thus, a solution requires that no two queens share the same row, column, or diagonal. There are 92 solutions. The problem was first posed in the mid-19th century. In the modern era, it is often used as an example problem for various computer programming techniques.

The eight queens puzzle is a special case of the more general n queens problem of placing n non-attacking queens on an n×n chessboard. Solutions exist for all natural numbers n with the exception of n = 2 and n = 3. Although the exact number of solutions is only known for n ≤ 27, the asymptotic growth rate of the number of solutions is approximately (0.143 n)n.