This is a Melon puzzle. (23 – Sudoku +/- 4)

Sudoku +/- 4 by Palmer Mebane

PDF

or solve online (using our beta test of Penpa-Edit tools; use tab to alternate between Number entry mode and a shading mode to help track complete clues.)

Theme: Clue Symmetry, and Very Hard WPC Practice

Rules: Variation of Sudoku. Place integers from -4 to 4 into each cell so that each row, column, and region contains each integer from -4 to 4 exactly once. The numbers outside the grid represent the sum of all integers between that clue and the zero in that row/column. Some cells inside the grid already contain an integer but no sign is given. It is part of the puzzle to determine if these values are positive or negative. An example using -2 to 2 from the WPC instructions is here.

Answer String: Enter the numbers (ignoring sign) from left to right in the marked rows, separating each row with a comma (eg “123401234,431023412”).

Time Standards (highlight to view): Grandmaster = 10:00, Master = 16:00, Expert = 32:00

Solution: PDF

  • hagriddler says:

    Nice variant & smooth solve, made me think “why didn’t I come up with that variant” 🙂

  • Aaron Chan says:

    I guess it was a good idea that I skipped this during the WPC after all. Took me 2 botched solves and 30 minutes.

    • MellowMelon says:

      I think the WPC one was easier. In general, and unexpectedly, most of the practice puzzles I made exceeded the actual WPC round puzzles in difficulty.

      • Aaron Chan says:

        I still haven’t went back and do it yet. Maybe I should do that sometime.

        • Avatar photo drsudoku says:

          The presence of a lot more given numbers definitely made the WPC one easier (this puzzle actually started with just 2 givens but more were added before posting here). I did fail to solve Palmer’s correctly the first time at the WPC but I learned enough to do well on the real puzzle. This is the purpose of Palmer’s practice for me at least — learn some notation and what sticking points feel like to be overprepared for the competition puzzle.

  • Naama says:

    Beautiful!

  • Francis says:

    Fun, and fortunately my inability to consistently remember to mentally swap positive and negative for totals on the opposite side of a zero only caused short-term errors that were easy to back out of.

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