
 Administrator
Country : India    Administrator
Country : India  Details about NEW, HUGE, AND CHALLENGING  LMI Fun ContestDates : 4 ^{th}  7 ^{th} March
Instruction Booklet & Submission : Link
Author : Ivan Koswara
  tamz29
Posts: 225
Country : Thailand  tamz29 posted @ 20160228 10:54 AM I remember this type from Ivan's test a while back ;)   chaotic_iak
Posts: 241
Country : Indonesia  Well, the test didn't happen, but the type persists. Better than a Heteromino for Puzzle Marathon, I guess, even though it turned out to be too hard. :P   rob
Posts: 170
Country : Germany  rob posted @ 20160228 4:28 PM This looks great! From the title, I was briefy wondering if it's April aready :)   Jacoblance
Posts: 9
Country : United States  I had the same exact thought as you rob, especially remembering how chaotic_iak's FAST went.   tamz29
Posts: 225
Country : Thailand  tamz29 posted @ 20160228 10:02 PM First reaction was an April Fools as well.
Now that you've mentioned it  I got your tests mixed up.
Deception (that I test solved) happened but the Poset Fillomino was in another (which I also test solved) which didn't right? :/
Why not run that :) ??   chaotic_iak
Posts: 241
Country : Indonesia  No, it isn't a joke contest; I wouldn't be able to concoct that background story. It's an actual test, although it only has one puzzle (that is hard enough so you win't answer in 5 seconds or something), like XKiller. I might still make an April Fools contest, though...
Yes, Deception happened, but the other test didn't; lost motivation, mostly.   debmohanty
Country : India  rob  20160228 4:28 PM
This looks great! From the title, I was briefy wondering if it's April aready :)
Jacoblance  20160228 9:19 PM
I had the same exact thought as you rob, especially remembering how chaotic_iak's FAST went.
tamz29  20160228 10:02 PM
First reaction was an April Fools as well.
It is not a joke test, as Ivan confirmed. It will probably be exactly opposite, with a very challenging (at least, as per the test solvers ) puzzle. The puzzle will be a 16X16 grid, with at least 93.75% empty cells. [Thats a good thing about fun contests, I can reveal all these information ]   Administrator
Country : India  Some notes1. There is no contest duration for this one. After you start, you can submit until the end of contest.
2. Link to score page : http://logicmastersindia.com/2016/03F/score.asp
You can view the score page at any time (e.g. before participating ). This will give you an idea of how long you would take.
3. There is no bonus. The score page will be sorted by Submission time, including penalty time (2 minutes per each incorrect submission ), if any.
4. There will not be a feedback page, please leave any feedback in this post directly. You can also rate the puzzle.
5. This thread will remain restricted after the contest starts, if you want to discuss about the puzzle.
6. This contest will not be included in LMI puzzle ratings.
  rob
Posts: 170
Country : Germany  rob posted @ 20160304 1:57 AM Thanks, great marathon puzzle. It seems the difficulty is similar to my marathon Summon from last year, but let's see how fast others can go.
It took me a little too long to see the parity argument, after that it was a tricky but smooth solve.   debmohanty
Country : India  Restricted the thread and restored Rob's original comment.   Para
Posts: 315
Country : The Netherlands  Para posted @ 20160304 12:54 PM rob  20160304 1:57 AM
It took me a little too long to see the parity argument.
I had the same problem. I also missed one 4 cell chain that really got me stuck for ages as when I finally spotted it all of a sudden I started actually filling the grid. Edited by Para 20160304 12:55 PM
  Kithyane
Posts: 49
Country : France  Loved this puzzle !
It all went down to noticing how to attribute one of the 3 distincts chains to all cells, and then solve each chain mostly separately. The fact that each chain had a type (odd, even, double) was considerate of the author ! (I feared a completely random order, which would have artificialy made the puzzle harder)
Thank you very much for this fun moment :)   forcolin
Posts: 171
Country : ITALY  Excellent puzzle, thankyou, but definitively too hard for the marathon.
i kept staring at the grid for about 1 hr and I was thinking of giving up when I saw the light   justinlam3
Posts: 8
Country : Hong Kong  Great puzzle, Thanks.
A bit hard at the beginning but get really smooth solving while having labeled for the top ones (9,14,16,15,8).
  auroux
Posts: 144
Country : France  auroux posted @ 20160307 4:17 AM Wow. Excellent puzzle, but indeed, it would have been too hard for the marathon.
Am I the only one who hates the typesetting of Futoshik puzzlesi (not just this one  in general) and feels that a different notation (e.g. thermometer style) would make life a lot easier? I spent 15 minutes just trying to read the grid to find all instances of the pattern I was looking for, then another 15 minutes trying to solve based on that and breaking repeatedly before realizing that I had read one of the inequalities backwards...
Then at 45 minutes into the solving time I finally realized that I was being dumb and had missed the one crucial observation needed to make real progress on the puzzle. There were a lot of good ideas in the puzzle, excellent design overall!
Denis   Kithyane
Posts: 49
Country : France  Same as auroux, I struggled a bit to get used to the looks of the puzzle, but more due to the color of the lines (light grey) than to the symbol used. I think thermometerlike would have help noticing the "lines of 4", but would have been messy in other places (especially the center). I did read a few backwards too, but fortunately noticed it before using them.
I keep wondering, with does the 6x6 center square have blacker lines than the rest ? It did trouble me a bit (my brain kept trying to do some "sudoku like" reasoning with constaint on squares), and I find no logical reason for it even afterwards ?
  chaotic_iak
Posts: 241
Country : Indonesia  The center square spells LMI with the signs, albeit rather small, and the M is lower than L and I. The choice of light gray is unfortunate, yes, but I couldn't think of another way to highlight the LMI theme in the center otherwise.
Comments regarding the solution will be postponed until this is done.   BohemianCoast
Posts: 16
Country : United Kingdom  I enjoyed it, and finished it just a little too late for the contest (I made a small error, and by the time I'd spotted it and corrected it, it was done). It took me far longer than it should have done to spot the parity argument; having done that and with what I'd already observed, it was straightforward. I found the LMI in the centre very distracting. Thank you! Looking forward to the marathon now...   chaotic_iak
Posts: 241
Country : Indonesia  57 of 120 people that started the puzzle managed to successfully crack this puzzle. Congratulations for Endo (1st), Hideaki (2nd), and Prasanna (3rd) to take the podium. More complete statistics, including intended solution (mostly the opening), will come after I'm done with classes (read: a few hours).   chaotic_iak
Posts: 241
Country : Indonesia  Now that I have some time to make a better reply:
There are 120 people that started this test. 57 of them succeeded to crack the puzzle. 16 of them took more than six hours, so that's the progress of chipping away here and there, continuing to go through even when the odds look small. Special mention to Rakesh Rai (55th, 48:51:59) which had 27 incorrect attempts before succeeding. Only one of them managed to crack this puzzle in under an hour, which means Endo Ken (1st, 00:41:07) would be the only person with bonus had this puzzle appeared in the Marathon. Hideaki Jo (2nd, 01:01:13), Prasanna Seshadri (3rd, 01:01:35), Walker Anderson (4th, 01:02:30), and Yuhei Kusui (5th, 01:04:00) are just a few minutes too much from breaking the onehour mark, but at least they managed to take the top five positions. Congratulations for Japan to have the most finishers (15 out of 18), even though USA has more participants (8 out of 23). At this moment, the puzzle is rated 9.11 out of 10 from five players; I'm not sure how it can happen (with five ratings, the result should be a multiple of 0.20), but regardless, thank you for the positive reception.
Aesthetics is simple. The givens are there just because it looks nice, several tilted squares in a tilted square pattern. Believe it or not, I put them that way before deciding about the breakin (see below). The center square spells out LMI; this is also a necessary touch due to logical reasons, not just because I can fit such theme. (The original draft had the entire grid partitioned into 2x2 squares, just like what you see around the grid now, but that can be proven to be nonunique.) Yes, the choice of light gray borders for the rest other than the center was a poor choice; I couldn't think up of another way to highlight the LMI theme, but it's already done, so oh well.
The logic is tough. Of course, this is a challenging puzzle; the title even spells it out. (Yes, the title of the test is "NEW, HUGE, AND CHALLENGING".) The breakin is the toughest point:
1. Notice that since the 10s are all given, and it's at the bottom of the graph, we can effectively remove it out.
2. Suppose we group the numbers into odds (1,3,5,7,9), evens (2,4,6,8), and tens (11,12,13,14,15,16). Then x < y implies that x,y belong to the same group; there's no path between two different groups. (Not even using the 10, because that would require you to go down, then up again, so you won't follow the directions.)
3. Thus, we can divide the grid into regions; each region has all their cells connected to each other by some chain of inequalities. For example, everything but the middle 4x4 square is partitioned into 2x2 squares; those containing the 10s are further partitioned into Lblocks. In each region, all its cells must have numbers belonging to the same group.
4. This is Crazy Pavement logic. Along the first row, there must be 5 odd numbers. However, almost all the regions contribute two squares to it; the only region that doesn't is the Lblock in R12C56. Thus, this Lblock must contain odd numbers (otherwise we can't have 5 odd numbers).
5. Apply the same reasoning over rows 2, 3, 4, 13, 14, 15, 16, and columns 1, 2, 3, 4, 13, 14, 15, 16. Now all the Lblocks contain odd numbers.
6. Note that if a < b < c < d, then a,b,c,d are all odds or evens; there is no chain of four numbers in the tens.
7. In the first two columns, there are three 2x2 regions with a chain of four numbers, located conveniently at the topleft corner (so you hopefully can notice them early). Thus they all are odds or evens. This, together with the two Lblock regions in the same columns, identify all cells containing the odds and evens.
8. Which of the three 2x2 blocks in the first two columns can contain the odds? It cannot be R56C12, since it would force R12C12 and R34C12 to be evens, and thus would force R1C1 and R3C1 to be both 8. Thus R56C12 has even numbers.
9. Continuing from before, R12C12 cannot have the odds either; if that's the case, row 2 doesn't have any place for the 1. (All odd squares in row 2 are identified, namely R2C1,2,5,6,7. All of them are greater than some other number, so they can't be the 1.) Thus R12C12 has the evens, and thus it forces R34C12 to be the odds.
10. Since R12C12 has the evens, that means R1C1 has to be 8. This rules out R12C34 to be evens (it would make R1C4 to be 8 as well). Since it's a chain of 4 squares, it thus has to be odds.
11. A similar deduction of steps 710 happen in the last two columns.
That completes the opening. The rest of the puzzle, while pretty tough, is nowhere as difficult as this, as long as you keep track which cells are odds/evens/tens. You might apply step 6 a few more times to rule out a region from being tens.
Note that the graph is made of 10 at the bottom, then the odds and the evens in a linear order. The tens form a divisibility graph; if you throw away the 1, the rest is the same graph in one of the practice puzzles, where x < y means x divides y.
The LMI theme is there because, if not (I keep the 2x2 everywhere theme), you can't distinguish 12/14 and 13/16. There can't ever be 12/16; this can be proven. After so, we can just remove that arrow, and now 12/14 and 13/16 are indistinguishable, requiring me to add more givens. That would break the aesthetics.   debmohanty
Country : India  chaotic_iak  20160308 9:21 AM
At this moment, the puzzle is rated 9.11 out of 10 from five players; I'm not sure how it can happen (with five ratings, the result should be a multiple of 0.20), but regardless, thank you for the positive reception.
It is weighted by LMI ratings, just like it is done for other contests.   rakesh_rai
Posts: 774
Country : India  chaotic_iak  20160308 9:21 AM
... 27 incorrect attempts before succeeding... I had (confidently ) deduced the 2x2 boxes in R14 C912 wrongly (exactly the opposite of the actual solution ). And the grid allowed me to continue a long way, before getting a contradiction in the 1116 range. In these columns, R12 and R34 had the same set of inequality signs, and this induced the mistake. And this error took a lot of time to "undo".   prasanna16391
Posts: 1753
Country : India  I'm really surprised by my position in this contest. My printer gobbled up 10 randomly placed inequality signs, so I first had to slowly scan the PDF and place them (and keep the PDF open all the time just in case I went wrong). Then for some odd reason, I used triangles to mark the 13579 group when I usually use circles, and when it came to filling in this group later I realized that I'd made some of the triangles too small and spent a few more minutes erasing the smaller triangles (while keeping an eye on the PDF to make sure I didn't take away more inequality markings). I wouldn't have defeated Endo, but its nice to know I might have had a 'marathon bonus' on this puzzle if external factors hadn't played a part in it the way they did.
The breakin was really cool and while I expected some more solvers to see it quickly I did expect there to be many DNFs which is a good reason to not have it in the Marathon. But as a fun contest, well this was a lot of fun :)   debmohanty
Country : India  Password removed and solutions appended.
Thanks Ivan for a great puzzle (and also for the neat write up). I'm not sure how you felt when we "rejected" this one from Marathon, but now I'm very glad we did that.
Thanks also to Branko for testing this.   debmohanty
Country : India  prasanna16391  20160308 2:12 PM
I'm really surprised by my position in this contest. Congratulations for doublepodiumweekend.   aclayton
Posts: 3
Country : United States  Spent a rainy weekend periodically fiddling with this puzzle, trying to find a break in.. I marked the 2x2 region divisions, found and marked with various colors the 4 and 3chains, but eventually put it on hold until the end of the contest, figuring I'd find the hint I needed from the thread comments. I think I would have eventually realized what each 2x2 quartet belonging to a single leg of the number map implies for categorizing and placing the quartets, but my thought process never really came near the direction required to realize the parity breakin.
However, getting stumped was not discouraging at all, I knew from looking at the puzzle (and from Ivan's past puzzles) that it would eventually be enjoyable, and I patiently waited out the contest duration. Sure enough, by about bullet 3 or 4 of Ivan's great breakin explanation, I was off to the races. And was happy to find that all the cellcoloring work I had done earlier was not wasted, and very useful during the solve process. As expected, an extremely fun solve after getting over that first hurdle. Thank you Ivan!   romanm44
Posts: 3
Country : Canada  I believe there is a somewhat simpler way to determine that the Lblocks must all contain only odd numbers.
If one looks at any row (or column) of 2x2 blocks, there are 6 blocks each containing 4 values and 2 Lblocks each containing 3 values (when the 10s are excluded). In these blocks we need to place 10 odds, 8 evens and 12 tens with the restriction that each block can only contain values of the same type. The only way the odds can be accommodated is by using one 4block and both Lblocks. The remaining groups fit comfortably in 2 and 3 4blocks respectively.
I still can't understand how anyone can solve this puzzle in 41 minutes! :) 
