$/**$

$*$ Check if assigning value to houses$[$h$][$a$]$ is valid

$*/$

public boolean valid$($int$[][]$ houses, int h$,$ int a$,$ int value$)\{$

$//$ Use each value one time per column

for $($int i $=0$; i $<$ houses.length; i$++)\{$

if $($houses$[$i$][$a$]==$ value$)\{$

return false;

$\}$

$\}$

$//$ Provisional assignment

houses$[$h$][$a$]=$ value;

$//$ Check the constraints

boolean constraints $=$ britLivesInRedHouse$($houses$)$

&& swedeKeepsDogs$($houses$)$

&& daneDrinksTea$($houses$)$;

$//$ etc.

$//$ Undo test assignment

houses$[$h$][$a$]=$ NONE;

return

Start with only the britLivesInRedHouse constraint. Run your search and

verify that you can produce a solution with the Brit in the red house. The

other assignments will probably be incorrect, but that$$s okay.

$$ Then add one more constraint, like swedeKeepsDogs. Run the solution again

and verify that you$$re now satisfying both constraints.

$$ Continue, adding just one constraint at a time until you have all $15$ in place.

Who owns the fish