Analysis of the iPhone game Drop7 with tips on advanced strategy

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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!

Comments

[Jason Hill]

Hello. I just read your strategy guide and I'll got some things to add to it. I've kept some notes while I've played the game and here is what I've found out:

Longest sequence so far: 7-39-109-224-391-617-907-1267-1701-2213
Times I've cleared the entire board during a game: 1 (Do this early. After level 5, focus on chains, after level 20, focus on survival.)
Highest level so far: 34

It seems that after a certain level the circles remaining stop at 5. In essense it becomes like the hardcore mode. It never goes lower than that. So if you play hardcore mode, you can practice for the higher levels of normal.

I hope that helps a little. My highest score is 311 309.

[Nick Seeber]

Thanks Jason! A number of useful points... I'll update the article with the information in your comment.

You're right about the number of circles stabilising at 5 - just noticed in the screen grab above (at level 27) it's at five - according to my predictions it would be at 3... :-)

Re. the scoring increase, there clearly isn't an even pattern - I had extrapolated beyond 617.

I've also only ever cleared the board once (it was the second time I played and I thought that it was something that happened often - proved to be very wrong.

Anyway, thanks again and let me know if you think of anything else.

N

[Solotoj]

Any strategy hints for hardcore mode?

[Nick Seeber]

@solotoj

No, afraid not as I havent really played it much. But Ive been told its like the later stages of the standard game - so all about making the most of level-ups...

Post some hints here if you discover anything!

Nick

[Nitpicker]

Great post! Nice to see someone applying such a scientific approach to a puzzler ;)

I take it you mean that the best strategy for Hardcore mode is pure 'Survivalist' (and not pure 'Chain-builder, like you've written).

I play mostly Hardcore, and am consistently achieving scores in the upper 200,000s. This is almost entirely from level-up bonuses, though. In hardcore mode that is 17,000, and in my latest game I achieved a score of 293,764, getting to level 18. That means just 4,764 points came from chains...

My high score is just above 450,000. I might have gotten a few more chains then, I don't remember which level I got to, but probably not a lot.

Strategy-wise, I haven't come up with too much, but here are a few points:

- When starting, I avoid explosions until the first level-up, and try to maximize the number of explosions to clear the first gray row. From then onwards, it's all about getting rid of as many gray balls as possible.
- I try to avoid #6s on the first and seventh column, since it's a bitch when you get one in both of those.
- I watch out for any number which is lower than my lowest column. E.g. if all my columns have five balls or more, I try to make sure I get rid of a #4 as soon as possible.

I am VERY curious as to how people achieve scores over 1 million. Do they do more chain-building, or are they just better survivalists than I am?

[KennyK]

Great blog! I've noticed (IMHO) that low numbers are very friendly critters in the early going and become increasingly dangerous as the game progresses. In a purely survivalist mode, the two and the three are very powerful in that they take little effort tto explode, are easy to predict, and give you and are good for clearing the 1&7 columns which to me at least, are the most critical columns to keep clear. Keeping the 1&7 column clear allows you the flexibility to build larger chains as they keep the early sixes and fives exploding in chains. That's why I almost always seek to place 7's inthe first or last columns as they provide protection that you won't accidently fill them. When the 1&7 columns are both occupied then those nice powder blue sixes become impossible to explode unless
you either clear 1 or 7, or go vertical. That being said I believe planning the freeing up of a full 1 or 7 column at a strategic point gives you the opportunity for large scale chain explosions. If your sixes and fives are spaced properly on the inner columns then they can be set to explode in sequence as soon as either the 1 or 7 column get cleared.
Other small observations I noticed include:
- try making sure your new gray blocks aren't allowed to bunch together. This sounds odd being that the level increase brings you 7 bunched greys but I will rarely drop a grey bloc on top of another. This is because the grey circle is not known thus can't be relied upon in chain building. So when I drop numbered circles, I usually leave an open space between them for new gray circles.
- don't allow fives to become separated (horizontally) by more than five squares. Otherwise they can't be triggered together in any one row and stay that way until you clear one off the row. That can only be done by getting stuff done under one of the fives.
- don't be afraid to use twos and threes above the second and third rows. When employed properly they can provide critical, predictable timing for long sequences.
- to maximize the probability of a cleared board be careful on the placement of your 2,3&4's as they will often explode prematurely costing you valuable opportunities to clear before the next level.

Hope this helps.

[Nick Seeber]

Thanks Kenny! Great post with lots of info and tips.

Re. your point on properly spacing 5s and 6s to get a chain reaction going, can you get a screen grab to illustrate what you mean? I think that a lot of people would be interested in seeing that. Or a more specific description of how to design chain reactions...

Thanks again -

Nick

[redoak]

Very helpful. Thanks.

One strategic approach that I often follow involves building stacks of sixes and sevens. The sevens go in one of the end spots and the sixes in the column next to it (or in the other end spot). As long as I leave a space open in the base row, I can build the sixes up as high as five spaces and the sevens as high as six. When I fill in the open spot in the base row, the sevens come down one at a time, followed by the sixes. Executed properly, that should get you a chain of eleven. And if you can position a few fives in the middle, you can get even more out of it.

By the way, I've never gotten the full mileage out of this strategy. Usually I have to bail and trip the trigger before the level change does it for me and take away my stack of sixes, for example.

[Nick Seeber]

Thats really interesting, thanks redoak. I will be trying that later...

N

[thread314]

Great suggestions, I will be trying them all out.

Expanding on Redoaks point, you could also then make a four-high column of fives, a three-high column of fours, a two-high column of threes and then two separate one-high columns of twos. This would be a chain of 21 (6+5+4+3+2+1), the longest possible chain you could ever make.

Of course, the conditions required to set this up would be extraordinarily unlikely, but still it's a dream of mine to see it.

Interesting reading, nice to know other people have spent as much time strategising over this amazingly addictive game as I have. Would love to pick the brains of those who regularly get 400,000 +.

[Nick Seeber]

Thanks thread314 - agreed that seems fairly unlikely but good to know
its theoretically possible! If you do get an outstanding chain,
please do post a screenshot, too.

Cheers

Nick

[SiKotic]

Great article!
I've been playing this game for 6+ months now, I got hooked straight away and then had some time out, but over the last few weeks I've got bang on it again. I also got my brother hooked, only he doesn't have an iPhone so we take turns.

I quickly got sick of waiting for my turn so I forced us to play hadcore mode despite not liking it as much. Now though, I find normal mode too slow, as does my brother. I strongly urge you to make the switch and stick with it for a while.
Recently we have been discussing changing strategies which lead us to this site.

My highest score on Normal mode is 435,000ish and my highest score in hardcore mode is 527,000ish. I tend to get between 300-400,000 in hardcore mode for most games. I would like to challenge the theory that chain-building is the way forward in hardcore mode as I rarely get above 6 as my longest chain. I try to keep the board as clear as possible. I think the most important thing is to not worry too much about grey circles on the top row (that's where 1s and 2s are in their element) but as soon as I create a gap in the top row, I focus on capitalising on it.

In normal mode I agree to reserve the end columns for 7s, the next column in is for 6s, then the next for 5s. Destroy 1s ASAP, though they do come in useful (ie next to a lonesome 2) and make good triggers. I build horizontal lines and stack matching numbers so they drop into place to create chains. Like someone mentioned earlier, place numbers in every other column if you can so grey circles can be dropped inbetween.

I'm open to any other suggestions or comments as I just can't comprehend how people are breaking the 1million mark.

[Nick Seeber]

Thanks SiKotic - you've inspired me to get back into Drop7 again and try Hardcore mode. However I'm really struggling to break the 300k mark! Probably just needs more time and effort...

PS thanks all for the comments - I checked my sites' stats and this post gets by far the highest referral traffic. Not that I get any revenue from it (this site's just a hobby), but nice to know it's been useful.

Cheers,

Nick

[SiKotic]

Glad I could be of service!
I found this page through the official Drop7 forum, and this is by far the most comprehensive article on the game.

I'm going to be checking back to see if anyone posts anything else on here so let us know how you get on with hardcore mode and if you develop any strategies. I'll let you know if I have any breakthrough's.

I think it is just time that will get you over 300k as you get used to the fast paced version. I am happy when I score over 240k. I can't believe the high scores are 800k-1 million plus.

My main focus is actually increasing my average score, but since I was so terrible to begin with and have played a lot of games, it doesn't budge much.

[Steve]

Hey guys, huge Drop7 fan here. I basically only play Hardcore these days as Normal mode takes too long, with my highest score being 940,921 (currently ranked #41 all-time!). However, note that this is only after thousands and thousands of games.

I have to say that most games end in bunches of 1s and 2s at around the 300k mark - that seems to be the most common average score. You have to be pretty lucky to get beyond that, as the game seems to like screwing you over by creating 3 or 4 1s in a row at some point when you level up. When I got my all-time high score it was as if I couldn't die - literally every grey circle I broke seemed to chain nicely into the next one, and I never got stuck, I just couldn't believe it.

So while there are techniques to it, I don't think there's any way of making certain you get a high score. There is some skill involved in knowing how to set up good chains and not get yourself stuck, but the game can and will kill you at some point. You just have to be lucky for it to generate good grey blobs with each level up. Strangely, despite the luck element, I still can't stop playing it!

[Nick Seeber]

Thanks Steve - I think your high score makes you a celebrity on this thread! 940k is massive :-) am also glad to know it's all luck ;-)

Likewise am only playing Hardcore these days but my high score is a measly ~350k and I'm pretty happy when I get over 260k. Getting 300k on average would be awesome! Having said that, I've only just started playing it so am probably at the ~100 game mark.

Anyway, thanks again for your comment and good luck with beating your own record - 1,000,000 must be a tempting target!

[Tom Purves]

Top score 994k here. Only play hardcore. Normal takes to long, and sequence I only played 3 times. The third time by fluke I cleared the deck twice(!) and realized I would never have a game this good again (>640k or so) and immediately gave up on playing sequence again. Fyi: how you clear the deck twice in one game is that you do it once and the next number that falls is a 1.

Agree with Steve, there is a lot you can do in this game to finesse your odds and use every number you can control to it's best potential. Each number has it's own character and strategy which evolves with the height of the stack. But you just can't control what is under the greys and if the random number generator want's to screw you it will screw you. My average score on hardcore is 270k after a few thousand games.

I'd like to see them release a version of hardcore where every sequence is almost always different but each one is known to have at least the potential of a high score.

Some tips: fight like hell to keep the whole stack under three rows tall, especially at the edges, and you can go far. Don't be afraid of the ones, you need all the ammunition you can get on hardcore. But! be careful of undermining ones and twos and letting them drop down too often. After a while they accumulate like sediment and once a bunch of low numbers join hands it will end a good game.

keep the 6's off the edges. Play the odds on the greys, sometimes you have to take chances to stay alive.

try not to get too obsessed. (good luck with that)

[Nick Seeber]

Thanks Tom. I've been playing Hardcore exclusively for about a month now - since SiKoTic's comment on 17 March! Since then I've probably notched up two or three hundred games, and my high score is about 500k (woop woop - though in comparison the next highest is 350k I think!). I was consistently getting about 180-190k until a few days ago when I made a few changes to my approach which have got me up to around 250-270k. They were:
- trying not to make any explosions on the first level, and setting up as best as possible for when the first grey circles arrived at the first 'level up'. This basically gives you a free level or two (17-34k) if you do it right.
- focusing on numbered circles as valuable resources to be conserved rather than gotten rid of as soon as possible (like Tom, I fight to keep the total rows low, but I try to only destroy coloured circles when they are exposing grey ones at the same time). Note that I'm NOT making chains (ie my advice in the article about Hardcore was totally wrong as I've suspected for a while!)

I will add in a new section on Hardcore incorporating all of your suggestions soon...!

[Giles Bowkett]

I have some videos doing the strategy that Redoak describes on my blog.

http://gilesbowkett.blogspot.com/2010/06/how-to-win-at-drop7.html

I take it even further - sometimes I work in a few fours. Usually not, though. Usually it's sevens, sixes, and fives. I also tend to stack lots of greys on top of the remaining columns, A) because it takes a while to build up six sevens, five sixes, and four fives, and B) because when they explode, they sometimes reveal digits that kill your chain midway through. If you stack stuff on top of them, you minimize the damage they can do to your overall plan.

Obviously six sevens, five sixes, and four fives add up to a total chain of fifteen. I think the highest number of points I've been awarded for the detonation of a single number is 3901, but I could be wrong; it could be higher. I have this feeling I've seen a 7000+ point award once.

Also, re: the 70,000-point bonus, I have before and after screenshots of that on my blog as well, same link. Your assertion that the million-plus people are not getting more than one 70,000-point bonus per game, I actually VERY much doubt. I've gotten it twice in the same game at least once, and when I got it in the screenshot in my blog, I got it **deliberately** - that is to say, I needed the screenshot to make a point, so I started playing and I had it set up in about five minutes. I haven't gotten so good as to get multiple 70,000-point bonuses per game, it's still mostly luck, but I'm absolutely certain it can be done.

Then again, I'm equally certain that fifteen-explosion chains are doable, because I've done them, or done similar numbers at least. Again there's a huge amount of luck involved, but it can happen. You say the million-plus folks probably get an average of ten explosions per chain; I don't get that, but I do get multiple ten-explosion chains per game. Imagine for the sake of argument that you work a couple fours into the mix; it's not easy, but you can do it. With fours the maximum theoretically possible chain length goes to 18, and the gains there would be extraordinary.

You can also get a bunch of free explosions by stacking 2s on top of higher numbers while you build your stacks. You can kind of treat the tops of the stacks as survivalist zones - i.e., if you have five sevens and four sixes, sitting right next to each other, and then you get a 2, you just put the two on top of the sixes, because it'll explode immediately. Alternatively, you can put it on top of the stack of sevens, and then it'll blow up as the stack collapses.

[Bucks]

Has anyone actually written out the entire order for the sequence game? I started but it makes it really slow to play. I know it's taking the fun out of it. But would be cool to have the exact order and plan a "perfect game"?

[Peter K]

Very interesting reading. I've been a big fan for about 18 months and have come back to this blog several times over that period. I play hardcore mode and yesterday scored an unbelievable 1.45 million, which gave me the highest ever score! Previous to this game my best score was in the 800s. As steve mentioned above a big part of getting the higher scores is luck. I use most of the techniques mentioned above but at the end of the day you can only do as well as the game allows you. Like somebody else mentioned, in this game the numbers in the disks continually gave me the perfect number and only a couple of times I got consecutive 1s. It actually makes it difficult to keep on playing as I know my chances of topping that score is next to nil. Anyway great article.

[Account Deleted]

@Peter K

>I play hardcore mode and yesterday scored an unbelievable 1.45 million

WOW. Thanks for letting us know, Peter, that's incredible - congratulations!

> Anyway great article.

Much appreciated - it's funny, it gets far and away more traffic than any other post I've written :-)

If you're thinking of moving away from Drop7, other games I've enjoyed on the iPhone are:

- Cat Physics (very addictive if you're a perfectionist!)
- Trainyard (great problem-solving and very satisfying when you get it)

Nick

[Account Deleted]

@ Bucks

No-one written out the Drop7 Sequence from that mode to my knowledge. I've just had a look through the Drop7 forum and it's not referenced there at all!

If you do get around to doing it (!) you're welcome to post it here!

Cheers,

Nick

[Kenny]

Hi,

I'm so relieved I'm not the only person who thinks (a) this game is awesome and (b) is trying to figure out how to improve my tactics :)

What I've learned: I'm a survivalist, and I should try to become a chain builder. I'm getting 200K scores at the moment.

Finally, I'm also glad I'm not the only person who has one post on their blog which gets far more traffic than any other written - mine is on iPod USB connectivity!

Cheers,

--
Kenny

[Teraisa Joan Ann]

Thank you for a terrific article AND for the fantastic comments and comment responses. I'm testing it all since I'm unable to get myself past 258k in ANY mode!

[Nick Seeber]

Thanks Teraisa! Im glad youve found it useful. I had no idea when I wrote this article quite how much traffic it would generate :-)

 

Good luck with your quest to break the 300k points barrier!

 

Nick

 

[Crowleystephen]

I've been playing this for a few months in survivalist mode and have just started to go towards chain building. My previous highest score was 318,000 and after just a few shots at chain building I managed 380,000.

I've tried the building 7s then 6s then 5s and yesterday it worked out extremely well. Managed to get a screenshot too - http://i.imgur.com/ts4TX.jpg the chain just kept going and I was above 70,000 points on level 2. Unfortunately it didn't work out but I'll keep trying. Great guide and comments!

[Nick Seeber]

Thanks Stephen! Im glad to see that the guide (and actually, the comments more so!) is still useful after all this time. Good luck with the ongoing challenge :-)

[Keshavsaharia]

This guide is great and I remember reading it about a year ago when I started playing. Drop7 is a fascinating game and if you're into programming, you might be interested in checking this out:

http://keshavsaharia.com/2011/01/09/drop7/

It's basically a recreation of the game in Java, upon which brute-force statistical tests were applied to find the optimal move. Obviously, not practical for the casual drop7-er, but a fun read for anyone who is really into the game.