If you have a finite number of puzzles, you can:
- Build a list of puzzles, either all of them or some randomly picked;
- Shuffle this list (see the Knuth Shuffle for instance);
- Let your player play through this list;
- When the list is empty, start with a new one.
EDIT
I didn't know this, but browsing SE made me realize that this is actually known as a "shuffle bag". Some more infos here, here or therethere.
EDIT 2
The classic Knuth Shuffle goes this way:
To shuffle an array a of n elements (indices 0..n-1):
for i from n − 1 down to 1 do
j ← random integer with 0 ≤ j ≤ i
exchange a[j] and a[i]
Steven Stadnicki rightfully pointed out in his comment that this kind of thing doesn't prevent repetition on a reshuffle. A way to take this into account is to add a special case for the last item:
To reshuffle an array a of n elements and prevent repetitions (indices 0..n-1):
return if n <= 2
// Classic Knuth Shuffle for all items *except* the last one
for i from n − 2 down to 1 do
j ← random integer with 0 ≤ j ≤ i
exchange a[j] and a[i]
// Special case for the last item
// Exchange it with an item which is *not* the first one
r ← random integer with 1 ≤ r ≤ n - 1
exchange a[r] and a[n - 1]
