Purpose

On ShopTo.net, top-up cards (with values ranging from £5 to £100) for the PlayStation Store can be bought at a discount from their nominal price. However, the discount isn't consistent across all cards; the savings can vary depending on the combination you buy.

How do you know if you're buying the cheapest combo?

This program solves that for you!

Getting it working

No additional files required!

The only thing you will probably need to do is change the prices in the list costs. It's simple, though. The cost of topups[x] = costs[x]. I've ordered the top-up values in descending order by default, but they can be changed around. All that matters is that the corresponding top-up and cost are in the same index of topups and costs.

It is IMPERATIVE that this is done carefully.

How to use it

Just input the amount you to wish to top-up your Wallet with (no currency signs!) and let the program work it out for you. It'll tell you the cost of what you're buying, and how much you're saving, both in cash and as a percentage of the standard price.

This will continually loop until you close the program.

Things to watch out for

• This only works for multiples of £5.

  • I will update this so it works for any positive, non-integral inputs up to two decimal points.

• MASSIVE SLOWDOWN past £100 or so. Without removing duplicates, it seems len(matches) (the number of combinations) doubles with every £5 added.

  • £90 gives 130K combinations, £105 gives 1.04M, £120 gives 8.3M, etc.
  • If I don't dedupe matches (containing all combinations), it slows down lowest() in calculating the total cost of each combination in matches because there are so many redundant ones.
  • If I dedupe matches, that process becomes the rate-limitng step, though len(matches) shrinks by several orders of magnitude.

• I'll run loop testing to see which is faster. I imagine the latter would place less strain on memory, so I'll default to that method.

  • Maybe running it on a 12-inch MacBook (2017) with a 1.4GHz Dual-Core i7 is the actual problem...

Future

I'm considering making a separate revision that scrapes ShopTo.net. Benefits would be threefold:

• Bonus points for functional complexity!
• QoL: the user wouldn't have to hard code in the current values (they change regularly).
• Erases possibility for human error messing up the code itself when adjusting costs.