Dr. Sudoku Prescribes #4 – TomTom

TomTom for 1/3/13 by Thomas Snyder


or solve online (using our beta test of Penpa-Edit tools)

Theme: TomTom for 1/3/13; there are also a few interesting and unusual logical deductions to be found.

Rules: Standard TomTom rules.

Answer String: Enter the 2nd row from left to right, followed by a comma, followed by the 6th column from top to bottom.

Time Standard: TomTom Master = 4:30, Expert = 13:30, Novice = 45:00

Solution: PDF

Note: Advice on solving this puzzle has now been posted in “Ask Dr. Sudoku #1“.

  • Ooof, that was a tough one for me – 23 minutes (why did I decide to start keeping time on THIS one???). I even had to use uniqueness on the left two columns just to break in (though it’s probably the nicest uniqueness proof I’ve come up with in a logic puzzle).

    • Avatar photo drsudoku says:

      The stack of left column clues does lead itself nicely to uniqueness (my puzzle “Big Chasm”, p. 58 in TomTom Puzzles is my favorite version of this exact trick). But of course I cannot construct using uniqueness so working through those columns with the 2 open options is how I tested this.

  • skynet says:

    53 mins and still not completed..i feel like i have been handicapped without the operations given..clueless in my second tom tom puzzle..hope to completed before evening

  • skynet says:

    what is this uniqueness thing that i see many people referring to ??????????is it something like a sole candidate for a cell???and what does someone mean by saying broken puzzle??

    • Avatar photo drsudoku says:

      When someone says a “broken puzzle”, they most often mean one that has either zero or too many solutions. “Uniqueness” refers to an assumption made with the hope the puzzle has just one solution.

      For example, if one of the 1 cages on the left side contains 65, and another contains 56, those could change to have two answers. So once you know one cage contains 65, no cage can contain 56. In this puzzle, that means the cage contains 54. Perhaps this is too confusing for you, but I suggest solving some of the “easier” TomTom linked to on the rules page. This one is hard for a second puzzle.

  • Para says:

    3:30 Still a master. I liked it, smooth solve. Maybe I’ve done enough to not that quickly get stumped.

    • Avatar photo drsudoku says:

      Thanks Para. Since this has an unusual break-in, it is hard to time. Certainly the experienced solvers will have a leg up.

      I’ll be curious to see your Saturday time, but you may be the first to have a clean sweep in TomTom.

  • tamz29 says:


  • TheSubro says:

    Possibly favorite TomTom ever. Seemed impossible at first, but unfolded in layers. I did use the uniqueness trick on the left hand side as well. Try to avoid that except in competitions, but it just jumped out at me so loudly while there was “silence” everywhere else.



    • Avatar photo drsudoku says:

      One of my favorites for the same reason. But it does lead to the “Ouch” comments and other frustration above. I’m waiting for someone to say, like one of my brilliant test solvers, that they “used parity” and not “used uniqueness” to do something in the second column to get cracking.

  • hagriddler says:

    What do you mean by “used parity” ?
    Is that when one of the 1 cages is say 65 another 1 cage must be 43 because 45 is no longer possible ?

    • Avatar photo drsudoku says:

      The deduction you should be able to make is this: because the numbers in R1C1 and R6C1 are both odd, the numbers in R1C2 and R6C2 are both even as a consequence of the four 1- cages in those two columns in the other cells. This gives you R1C2 and R1C3 and getting R1C3=5 is critical to breaking in.

  • hagriddler says:

    Ah, without explicitly realising the parity property
    of the candidates in C1, I started with the possibilities for the four 1 cages, which gave me the same break in for R6C2/R1C2/R1C3. So I guess I used parity more or less, without realising it… 😉
    Another nice puzzle ! Keep up the good work !

  • hagriddler says:

    A question about the use of the reply form :

    I cannot (in FF) use my mouse but only the tab key to fill in the fields in the form and click on PostComment.

    Also the link to the previous puzzle below this post form
    is with a mouse only partly clickable (only the text “Dr. Sudoku” is clickable but not “Prescribes #3 – Sudoku”).
    The link for the next puzzle is with a mouse not clickable. But using the tab key both links are fine.

    Has anyone the same problem ?

  • Avatar photo drsudoku says:

    I got a similar indication by email yesterday from another top solver, also just with Firefox. I’m trying to look into the issues to the best of my ability. With a new WordPress install, and the first real week of load testing, we are running into a few problems but dealing with them when we can.

  • Zotmeister says:

    Definitely took awhile to find the break-in: I don’t normally encounter a cage with five combinations reduced to just one without any intermediate steps. Mind you, one of those impossibilities requires examining the entire fifth row to see it, albeit in a good, clever way.

    Uniqueness of solution is definitely not necessary here, and in my solving path at least would not have been helpful either.

    The login widget doesn’t work for me – I’m still needing to sign in to The Griddle (curse you for making me register there!) in a separate tab.

  • Patti says:

    Took me exactly 30 min once I got the hang of it. Still a beginner although I’ve done some of the ‘KenKen’ puzzles.

  • swaroop says:

    Awesome puzzle,
    i didn’t knew we can use parity logic as well while solving in these kind of puzzles surely lot to learn.
    Thanks for beautiful puzzle

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