I’m sure many of you were expecting ANOTHER version of the Christmas Tree puzzle from the last two weeks. I mean, I did get a very nice Double Back from Robert Vollmert (which cannot be confused as a Star Battle or a LITS). But posting such a puzzle wouldn’t be a surprise.

No, today’s Sunday Surprise comes from the pile of submissions I’ve received over the year from Hans van Stippent, who played with the usual rules of Skyscrapers a bit by hiding some of the cells from consideration. It yielded a very interesting puzzle which is Hans’ gift to you this Sunday.

PDF

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

Theme: New Variation/Logic

Rules: Standard Sudoku rules. Also, standard Skyscrapers rules. Additionally, the cells in gray are “underground” and cannot be seen for any of the outside skyscraper clues (think of them as starting with a negative sign if necessary). As an example, the 4 in row 2 refers only to seeing four buildings in columns 3 through 7, even if there is a 9 in column 1 or column 2 as that 9 cannot be seen.

Answer String: Enter the 1st row from left to right, followed by a comma, followed by the 9th row from left to right.

Solution: PDF

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

PDF

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

Theme: Virginia is for Sudoku Lovers (Note: This puzzle was the final puzzle for this year’s Arlington Puzzle Festival. Congratulations to Erik Agard, Carolyn Offutt, and Jim Spaulding for their 1st/2nd/3rd performance in the tournament.)

Rules: Standard Sudoku rules.

Answer String: Enter the 1st row from left to right, followed by a comma, followed by the 9th row from left to right.

Time Standards (highlight to view): Grandmaster = 2:15, Master = 3:30, Expert = 7:00

Solution: PDF

Note: Follow this link for other classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on. More classic Sudoku puzzles can be found in The Art of Sudoku, The Art of Sudoku 2 and in our beginner-friendly collection Intro to GMPuzzles by Serkan Yürekli.

PDF

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

Theme: High and Low (Note: This puzzle was one of the qualifying round puzzles from this year’s Arlington Puzzle Festival)

Rules: Standard Sudoku rules.

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

Time Standards (highlight to view): Grandmaster = 2:15, Master = 3:15, Expert = 6:30

Solution: PDF

Note: Follow this link for other classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on. More classic Sudoku puzzles can be found in The Art of Sudoku, The Art of Sudoku 2 and in our beginner-friendly collection Intro to GMPuzzles by Serkan Yürekli.

PDF

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

Theme: Four-leaf Clover (Note: This puzzle was one of the qualifying round puzzles from this year’s Arlington Puzzle Festival)

Rules: Standard Sudoku rules.

Answer String: Enter the 1st row from left to right, followed by a comma, followed by the 9th row from left to right.

Time Standards (highlight to view): Grandmaster = 3:00, Master = 5:15, Expert = 10:30

Solution: PDF

Note: Follow this link for other classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on. More classic Sudoku puzzles can be found in The Art of Sudoku, The Art of Sudoku 2 and in our beginner-friendly collection Intro to GMPuzzles by Serkan Yürekli.

PDF

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

Theme: Logical (Note: This puzzle was one of the qualifying round puzzles from this year’s Arlington Puzzle Festival)

Rules: Standard Sudoku rules.

Answer String: Enter the 4th row from left to right, followed by a comma, followed by the 6th row from left to right.

Time Standards (highlight to view): Grandmaster = 2:00, Master = 2:45, Expert = 5:30

Solution: PDF

Note: Follow this link for other classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on. More classic Sudoku puzzles can be found in The Art of Sudoku, The Art of Sudoku 2 and in our beginner-friendly collection Intro to GMPuzzles by Serkan Yürekli.

PDF

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

Theme: Surprise Sudoku

Rules: Standard Sudoku rules. Also, there is a mystery rule that must be determined by looking at the example at the top of the puzzle.

Answer String: Enter the 1st row from left to right, followed by a comma, followed by the 9th row from left to right.

Time Standards (highlight to view): Grandmaster = 6:15, Master = 8:30, Expert = 17:00

Solution: PDF

Editorial Note: While this is an original sudoku for GM Puzzles, this particular “surprise” gimmick from Serkan first appeared on the SudokuCup 10 test with a different puzzle.

PDF

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

Theme: Two Rings

Rules: Standard Sudoku rules.

Answer String: Enter the 5th row from left to right, followed by a comma, followed by the 5th column from top to bottom.

Time Standards (highlight to view): Grandmaster = 1:30, Master = 2:15, Expert = 4:30

Solution: PDF

Note: Follow this link for other classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on. More classic Sudoku puzzles can be found in The Art of Sudoku, The Art of Sudoku 2 and in our beginner-friendly collection Intro to GMPuzzles by Serkan Yürekli.

PDF

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

Theme: Even/Odd Clover

Rules: Standard Sudoku rules.

Answer String: Enter the 1st row from left to right, followed by a comma, followed by the 9th column from top to bottom.

Time Standards (highlight to view): Grandmaster = 3:00, Master = 4:45, Expert = 9:30

Solution: PDF

Note: This puzzle is probably harder than a typical Monday, but was the style we always had in mind for 9/9, which the World Puzzle Federation recently set as “International Sudoku Day”. Happy solving! Follow this link for other classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on. More classic Sudoku puzzles can be found in The Art of Sudoku, The Art of Sudoku 2 and in our beginner-friendly collection Intro to GMPuzzles by Serkan Yürekli.

PDF

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

Theme: A Series of Falls — all 5 digits runs from 1-5 to 5-9 appear. (This puzzle also appeared on the recent Indian Sudoku Championship.)

Rules: Standard Sudoku rules.

Answer String: Enter the 4th column from top to bottom, followed by a comma, followed by the 8th column from top to bottom.

Time Standards (highlight to view): Grandmaster = 1:40, Master = 2:20, Expert = 4:40

Solution: PDF

Note: Follow this link for other classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on. More classic Sudoku puzzles can be found in The Art of Sudoku, The Art of Sudoku 2 and in our beginner-friendly collection Intro to GMPuzzles by Serkan Yürekli.