Undoc'd Feature?

[Albert Chan]

(07-03-2022 06:24 PM)Wes Loewer Wrote:  What an interesting little program. I cannot begin to image what it is trying to calculate. Whatever it is doing, it repeats the exact same calculation 1000 times, and a[0] never gets initialized or used.

Do tell, what is this?

It solve 8-Queen puzzle. (code really need comments!)

Code:

if (!(t=a[x]-a[--y]) || x-y==abs(t)) { ...

a[] is array of 8x8 chess board, a[i] = j      → Queen at (i,j)
a[x] is the newly placed Queen,
a[y] are previously placed Queens, y = 1 .. x-1

Since we placed 1 Queen per row, there is no need to check horizontal attacks.
We only need to test vertical attacks (1st test), and diagonal attacks (2nd test)

I would have return actual board (8-digit number), instead of steps required to solve it.
We could have returned same steps, but not really solved anything ...

http://users.rcn.com/liusomers/nqueen_demo/nqueens.html