This is the old Wolf, Goat, Cabbage puzzle for the ZX81. The major update was removing the INPUT commands to make it more interactive and to start over if failed or done.
This program was originally published in 1982 in the book “Computer Puzzles: For Spectrum & ZX81.’
JSZeddy, by Erik Olofsen based on JSSpeccy and Z81 emus.
For programs that don’t auto-run, press R then ENTER.
Also you may need to click on the applet to enable keyboard entry.