The **eight queens puzzle** is the problem of putting eight chess queens on an 8×8 chessboard such that none of them is able to capture any other using the standard chess queen’s moves. The queens must be placed in such a way that no two queens would be able to attack each other. Thus, a solution requires that no two queens share the same row, column, or diagonal. The eight queens puzzle is an example of the more general ** n queens puzzle** of placing

*n*queens on an

*n*×

*n*chessboard, where solutions exist only for

*n*= 1 or

*n*≥ 4.

https://en.wikipedia.org/wiki/Eight_queens_puzzle

I dug up some old code that implemented the puzzle solution(s) in scheme and x86 assembly.

- Scheme Source
- x86 Assembly Source, Base Algorithm
- x86 Assembly Source, All Optimizations
- x86 Executable

I remember trying to get solutions for large (over 10) boards in 1995 and my PC was a little slow. Things are very different today. Here’s an example of solution number 128570 for a board of 20.

```
(128570) 11 1 3 5 12 2 15 13 18 14 4 6 19 16 10 7 20 8 17 9
```