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I recently got the puzzle game Drop7 for my iPhone, and I've been playing it quite a lot for the last few weeks.
Obviously I've also been trying to work out what the optimal strategy is for improving my score, but oddly there isn't really anything useful on the Internet. As such I thought I'd write something, hopefully it's be useful.
Of course this probably won't be interesting unless you've played Drop7 before, but if you have an iPhone I would urge you to try it out. It's very satisfying and incredibly addictive...
Drop7's gameplay is much easier to learn than to describe and I'm assuming that most people reading this will have played it before, so I'm not going to spend too much time describing the rules - but there are a few things to focus on that influence how you can score high points.
Briefly, Drop7 is a bit like a cross between Tetris and Sudoku. You have a 7 x 7 grid into which you have to drop circles numbered 1 to 7, and the aim of the game is to blow the circles up in a way that maximises your score before the game is over. There's no time limit, so you can spend as much time as you like contemplating your next move. You get points in two ways: firstly, when circles blow up, and secondly, a 7000-point level-increase bonus.
Circles will spontaneously explode if the number in them is equal to the number of circles in that continuous line (either horizontally or vertically, not diagonally). For example, in the picture above, if I dropped the grey circle into the right-hand column, the three #7s would all explode at once. As circles explode, "gravity" will pull circles above them down towards the bottom of the screen -- which may cause other circles to explode, and so on - causing chains of explosions.
Chains of explosions are rewarded very highly, with the scores increasing exponentially with each step: the first circle(s) to explode score 7, the circle(s) in the next step of the chain score 39, then 109, 224, 391, 617, 907, 1267, 1701, 2213, etc. Suffice it to say you will score vastly much more by setting up a sequence that results in four circles exploding one after the other (7+39+109+224=379) than by blowing up four circles simultaneously (7*4=28).
A complication is that you can't always see what the circle's number is before you drop it onto the screen -- some circles are greyed-out (like the one in the picture above). These greyed-out circles contain numbers like all the others, but they are only revealed by causing circles immediately next to them (left/right/above/below - not diagonally) to explode. An explosion next to a greyed-out circle weakens it, and a second explosion reveals a number.
Each time the level increases, a layer of greyed-out circles move on to the screen from the bottom, pushing all existing circles up the screen. This means that level increases usually cause explosions to happen, and you can use this to your advantage by setting up chains of explosions when you get near a level increase. If any circles get pushed out of the top of the screen, it's GAME OVER.
Progress through a level is indicated at the bottom of the screen, where you can see how many circles you have left until the end of the level. On each level you're given one less circle than the previous level. The first level has 30 circles, and each subsequent level has one less, until at level 25 it stabilises at 5 cirlces per level and doesn't go any further.
All this means that there are some constraints which will influence strategy. NOTE: throughout this post I'm going to refer exclusively to NORMAL mode - for Hardcore mode the best strategy is totally different (pure 'Chain-builder' incidentally, more info below).
Firstly, no matter how good you are, your game will almost certainly end around level 30. Given that the number of circles you can explode per level is limited, and each new level adds new seven greyed-out circles, it's very difficult to survive beyond level 27 (in my experience at least!). I think that the highest level I've got to was 28.
Secondly, circles are limited. The game starts you with 10 random circles and 30 more drop onto the screen, so by the end of level 1 you've been given 40 circles in total; by the end of level 2, 76 circles; etc. Assuming that you survive to level 28, you will have had 661 circles - and if you've filled the screen before 'Game Over' you will have exploded around 610 circles. Each one of those explosions is a chance to earn at least 7 points - the more you score from each explosion the higher your overall score will be.
Thirdly, the ratio of greyed-out circles per level rises during the game. This is because a quarter of the circles from the top of the screen are greyed out (according to my sample of 100!), plus there are seven greyed-put circles at each level, so the proportion of greyed-out circles per level rises from 25% in level 1 to 69% by level 25 (and beyond)! Each of them require two other (numbered) circles to explode to reveal their numbers, so the number of explosions you have to generate just to keep up with revealing the grey circles rises. Making the most of explosions is therefore more important as the ratio of grey circles rises later in the game.
Finally, the number of "spare" explosions peaks during the middle of the game. This is because you need to "spend" two explosions to get each grey revealed. Assuming that you use two numbered circles to reveal one grey circle* then once the ratio of greys starts rising towards the end of the game, you'll struggle more and more to keep up.
(*I realise that you can use one numbered circle to weaken up to 4 neighbouring greys - this is a key part of my 'Survivalist' strategy below).
Simplistically, then, there are two basic strategies - 'Survivalist' or 'Chain-builder' depending on where you want to get your points.
A 'Survivalist' minimises the number of circles on the screen and always explodes grey circles as quickly as possible, and gets high scores by relying on the 7000-point level increase bonus. This is a low-risk strategy and one that I've used to get a consistent score of 200,000+ per game.
Survivalist tips include:
- get rid of #1s as soon as you can. They're a nightmare if you don't blow them up immediately and can single-handedly scupper a good game.
- explode circles as soon as you can and reveal greys quickly - basically, try to keep the screen as empty as possible.
- if you find yourself with a #1 stuck at the bottom, check the circles around it and try stacking circles with the same number on top of each other - this will eventually free the one
- later in the game (after level 17 when you start being short of explosions and the ratio of greys rises more quickly), try to be more efficient and maximise the use of explosions to reveal grey circles. I pack greys around #3s, #4s and #5s - ideally you want to have four greys touching a number when it blows up, so you're as efficient with your explosions as possible.
A 'Chain-builder' sets up sequences of explosions that result in very high scores, but at the cost of not blowing up the increasing numbers of grey circles on the screen. It's much more of a high-risk strategy as an elegantly designed sequence can be ruined by a single unplanned explosion that defuses the sequence and leaves you with a screen full of grey circles and few points. However when it goes right, you can get huge scores - shown on the Global high-score list this morning.
Two things to note:
a - Since the maximum points from level-increases is about 210k (30 levels x 7,000 point bonus), these people are getting ~300-400k points per game from explosions - that's around 500-800 points per circle! (Note: They could also be getting points from completely clearing the screen multiple times (each time you remove all the circles from the screen you get a 70,000 point bonus) but I think that's quite unlikely as it's rare and there are people on the high score list with multiple entries - that doesn't happy by luck alone!). This means getting average chain lengths of 10, which is astonishing.
b - As you can see, my overall ranking is pretty poor - and following the survival strategy isn't going to help me any further. I need to start getting points from chains...! And working out how to design consistently long chains. One method I've seen described to build chains is to simply avoid any explosions (except for #1s) and then allow the level increase to wipe out your screen. I'm not sure about this as my efforts with this strategy have been quite unsuccesful, but I'd love to hear from anyone who has ideas about how to make the most of it.
From my analysis I believe that the optimum strategy is a hybrid of the two above - to build chains whenever possible early in the game (levels 5-20) and then moves to a pure survival mode for the remainder. Ideally you want to be going into levels in the late 20's with a pretty much empty screen that will let you fill up slowly over the next 6-7 levels - to make the most of the level increase bonus - making sure that you get every last circle in that you can!
I think that this strategy has a nice blend of riskyness - though it requires some experience to work out how congested you can allow your screen to get during the early levels before you hit the event horizon - beyond which you won't be able to recover, and will crash and burn within a couple of levels.
Good luck, and let me know how you get on - specifically, if you have any good Chain-builder tips for me :-)
I'll post updates if I make any progress... Next target is 300k!