Dr. Sudoku Prescribes #51 – Slitherlink

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Slitherlink by Thomas Snyder


Theme: All for One and One for All

Rules: Standard Slitherlink rules.

Answer String: Enter the length in cells of each of the internal loop segments from left to right for the marked rows, starting at the top. Separate each row’s entry with a comma.

Time Standards (highlight to view): Grandmaster = 3:00, Master = 5:00, Expert = 10:00

  • ugh, rusty. I forgot the two 1’s on an edge rule. Remembering that broke the puzzle right open. That was a nice solving-theme.

  • TheSubro says:

    Ugh. 3:47.

    That’s not my time, that is how long I probably wasted in remembering and recognizing the 11 on end rule. Ended up 7:57 instead of what should have been 4:10.

    I will remember that rule forever now, or until I don’t again. :0)

    Thanks. Nice puzzle all around.


    • TheSubro says:

      Last comment on overlooking that “11 on end” rule. You only see it here in this puzzle if you are marking the board up with x’s as well, and after all of the back and forth yesterday on the topic, I tried to do it less than time than usually. Bit me in the arse. I will probably return to my overmarking as it actually seems to move me along best.


      • Scott Handelman says:

        Oh, absolutely. I was very glad that I marked everything for this one.

        Also, as soon as I opened the puzzle, I thought “Ah, the 1s are going to be used as a grand finale to make everything connect” and was surprised when the path through the 1s turned out to be one of the early steps.

      • Jack Bross says:

        Well, I marked a certain amount. The main thing that you need to remember is the “x’s” on the sides of those runs of 3’s, and I tend to just remember those automatically since they’re pretty common and easy to spot visually. So, yeah, you need to use “that string of ones would smack into a dead end because of the threes”, but I didn’t mark a lot in there.

        Really enjoyed the puzzle, Thomas! It’s not very often that I run into a Slitherlink that really makes me happy. If this were Nikoli, I’d be reaching for the “vote for the best” button.

        • drsudoku drsudoku says:

          Thanks for the comment. It makes me happy to hear it.

          While there is a “favorites” button here, and that top list matches what I’d call my best puzzles here pretty well, once other authors are contributing regularly I’ll figure out a way to reward the “best of the month” or equivalent.

  • Para says:

    Luckily I’m a fan of marking crosses. I like to put things in my puzzles as well, where marking crosses is really key to a quick solve because it creates edges and corners in the middle of the grid.

    I notice in the genres I grew up with solving like star battle, battleships and slitherlink I easily make the grandmaster times. I can afford some time to think.
    In the genres that are newer to me, which I really mainly now from online and puzzle competitions like nurikabe, masyu and cave I need to have a respectable solve to acchieve this. It doesn’t allow for mistakes. But maybe that’s partly because these are all Nikoli and more of your testers will have grown up solving these.

    • TheSubro says:

      Boy, do I feel old. Unlike Para, I “grew up solving” the daily crossword puzzle, and the daily “Jumble” game in the newspaper. If I was lucky, there was a word find puzzle.

      I do not believe that I saw a modern day logical spatial puzzle until Battleship in Games magazine in 1993 (when I was already married and 29 years old).

      Just sayin’


      • drsudoku drsudoku says:

        I’m not sure how Dutch compares as a language for the quality of its possible word puzzles. While America has been *blessed* (or insert other word) with a rich history of word puzzles, we lack the depth of other puzzle types other countries have that involve logic. I’m not sure what the 1980s picture would have been in The Netherlands but it would certainly be different.

      • Para says:

        Well I don’t mean grew up as in when I was a child, but grew up from when I got involved in solving WPC style logic puzzles. I started when I was 18.
        My first exposure to puzzles were crosswords too, although the standard crosswords weren’t my thing. I really started getting into puzzling when I discovered cryptic crosswords (with cryptic clues) and encrypted crosswords (where each letter is replaced by a number). I started doing these when I was about 12 with my neighbour as she always did those.

        My first exposure to more logic inspired puzzles were logiquizzes. The kind of puzzles where you are given a number of statements and have to match things together from different groups.

        There’s a long word puzzle history in the Netherlands. I think Dutch lends itself well for cryptic crosswords. Around the Christian holidays like Easter and Christmas most newspapers will print special Crosswords and Cryptic Crosswords. Some magazines will print thematic Cryptic Crosswords based on the theme of their magazine.

  • skynet says:

    38:42 s
    There is a thing or 2 i would like to share from a beginner’s perspective with respect to this puzzle
    I went through the slitherlink common patterns yesterday from paras puzzle site and i was thinking that this puzzle type was all about memorizing patterns and brushing it aside using the memorized patterns.I know i am very wrong now.
    Though the patterns did help me, for ex: the 3 3s successively in a row or a column , 3s diagonally present are all excellent starter rules .But then after that i was stumped .All i was looking for was patterns.30 mins wasted
    Then just one x near the 3 in the 7th row gave a chain reaction of Xs and the Xs began to proliferate fast in the 1 chunk in the middle.After that it was a smooth solve.
    So for beginners
    * Never forget the Xs in a slitherlink puzzle.
    * Memorizing patterns does not help always.
    And by the way what do u guys mean by the 1 1 rule???!!I dont see any rule of that sort or am i missing it?

    • Scott Handelman says:

      Imagine two 1s, side by side, on the edge of a puzzle. You know that there can not be a wall between them, because then it would be forced by the edge to move along the edge, but you’ve just used up the only wall around the 1s, so there’s no place for the path to go. So any time you see two 1s along an edge, you can mark an ‘X’ between them.

      The corollary of this rule is that it applies not only when there’s an edge, but whenever two 1s border a place that you’ve eliminated the possibility of a path. This happens a lot in this puzzle on the right and left sides of the square of 1s.

      (This would be much more easy to explain if I had pictures…)

    • Jack Bross says:

      What Scott is describing is the usual “1 1” rule. Here, there’s something a bit deeper happening that’s basically unique to the puzzle, and extends this rule a bit. You know there have to be some segments in the middle of all those 1’s, or the central 1’s wouldn’t have any edges. But any line segment in the middle of that block of 1’s must continue straight through the entire block and stick out at least one additional space on each side (so a minimum length of 6) by a sort of big extension of the 1 1 rule. This does not apply to segments along the outside of the block.

      Now, going back to the “3 3 3” patterns. The segments coming off the sides of one of those serpentine strings of 3’s are automatically x’ed out. ALL of the horizontal paths through the middle of the 1’s dead end at an x’ed out space and can’t continue for their full length of 6. In fact, the only path that can hit the 1’s in the middle of the third column of that block is a path vertically down the center of the block, which sticks up an additional square above and below (and on the bottom therefore gets snagged by the 3’s).

    • >> Memorizing patterns does not help always.

      Solving Slitherlink, probably more than any of the common puzzle types (except possibly Masyu), is greatly streamlined by knowing about 10 common situations that come up a lot (ie by “knowing rules”). But I think to be very good at Slitherlink, you shouldn’t memorize the rules so much as understand why they work. When I started with Slitherlink, I didn’t go look up the rules and memorize them. Instead, I forced myself to derive the results on my own. This helped me learn how to address situations that weren’t covered by the rules (or built on the simple rules) more flexibly, as well as building up a toolbox of rules. But eventually, using those rules should become second nature… You shouldn’t have to derive them every time you use them. It’s the difference between sounding out the letters in a word, and just recognizing the word and saying it automatically.

      Now, as I said above, I’ve forgotten some of the simple things, so I was a bit slow on this puzzle.

    • Para says:

      The reason I wrote the pattern guide was never to suggest that solving Slitherlink is just about memorising patterns. Actually the idea was a bit the opposite. Most of these patterns are just used to set up the basic structure of the puzzle and then the remaining numbers are used to finish off the puzzle. And those are where the beauty and fun of Slitherlink lie in.

      I didn’t include the 11 pattern as it’s not very useful in construction unless you make big areas with only 1s like in this puzzle. Otherwise it doesn’t contribute much.

  • Leaf says:

    Start with sixteen “1” and “33”. I wrote here.

  • Carl W says:

    I really enjoyed the opening of this puzzle. From the big block of central 1s I immediately “saw” only 4 possible patterns through that block, (2 horizontal, and 2 vertical), and quickly found where 3 of the 4 ran into problems with the 3 clues, (without even adding ‘x’s anywhere).

    I probably would have solved things quite quickly if I hadn’t proceeded to extend those quickly-derived lines too far along the corners of the block of 1s. It did take me some time to track that mistake down after it caused problems later on.

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