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Theme: Sudoku GP Round 7, plus two hidden themes related to 7
(Note: this puzzle was originally created for the Sudoku Grand Prix but after testing was judged too hard and too puzzle-based for the competition. It is an excellent puzzle, and we are proud to showcase it here.)

Author/Opus: This is the 40th puzzle from our contributing puzzlemaster Prasanna Seshadri.

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

Answer String: Enter the 1st row from left to right, followed by a comma, followed by the 5th row from left to right.

Time Standards (highlight to view): Grandmaster = 7:00, Master = 10:00, Expert = 20:00

Solution: PDF

Note: Follow this link for our first Basement Skyscraper Sudoku. Follow this link for other less common variations of Sudoku and this link for classic Sudoku. If you are new to this puzzle type, here are our easiest Sudoku to get started on.

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

Theme: No Givens

Author/Opus: This is the 5th puzzle from guest contributor Hans van Stippent.

Note: we’ve been holding onto this puzzle for awhile; it was inspired by last year’s USPC Thermo-Skyscrapers puzzle and, by adding in the sudoku constraints, makes a nice challenge before this weekend’s US Sudoku Qualifying Test.

Rules: Standard Thermo-Sudoku rules. Also, any digits in the thermometer shapes outside of the grid are Skyscraper clues, representing the number of buildings seen inside the grid in that direction as in a regular Skyscrapers puzzle. (Note: digits in a thermometer must be strictly increasing even when outside the grid, so do not repeat any digits within a thermometer.)

Answer String: Enter the 1st row from left to right, followed by a comma, followed by the 6th row from left to right. Note: only enter the 9 digits inside the grid in these rows, not any of the outside skyscraper clues.

Time Standards (highlight to view): Grandmaster = 5:30, Master = 9:30, Expert = 19:00

Solution: PDF

Note: Follow this link for more Thermo-Sudoku puzzles. If you are new to this puzzle type, here are our easiest Thermo-Sudoku to get started on. More Thermo-Sudoku puzzles can be found in The Art of Sudoku 2.

PDF

or solve online (using our beta test of Penpa-Edit tools; use tab to alternate between Sudoku = big digits and Number candidate = small entries in the corners of cells.)

Theme: Equal Distribution and Symmetry of Clue Numbers

Author/Opus: This is the 6th puzzle from guest contributor Roland Voigt.

Rules: Standard Skyscrapers rules. Also, some cells have been split into triangles, each of which must be filled with a number. In this puzzle, the numbers 1-6 must be placed in each row and column.

(The split cells are viewed in the order they are seen from a given direction, so the upper triangles are seen first from the left/top sides and the bottom triangles are seen first from the right/bottom sides.)

Answer String: Enter the 4th row from left to right, followed by a comma, followed by the 5th row from left to right. Enter the split cells in the order they are seen from the left (the upper triangle before the lower triangle).

Time Standards (highlight to view): Grandmaster = 6:00, Master = 9:00, Expert = 18:00

Solution: PDF

Note: Follow this link for other classic Skyscrapers and this link for variations on Skyscrapers puzzles. If you are new to this puzzle type, here are our easiest Skyscrapers to get started on.

PDF

or solve online (using our beta test of Penpa-Edit tools; use tab to alternate between Sudoku = big digits and Number candidate = small entries in the corners of cells.)

Theme: Equal Distribution and Pairing of Clue Numbers

Author/Opus: This is the 4th puzzle from guest contributor Roland Voigt.

Rules: Standard Skyscrapers rules. Also, some cells have been split into triangles, each of which must be filled with a number. In this puzzle, the numbers 1-6 must be placed in each row and column.

(The split cells are viewed in the order they are seen from a given direction, so the upper triangles are seen first from the left/top sides and the bottom triangles are seen first from the right/bottom sides.)

Answer String: Enter the 1st row from left to right, followed by a comma, followed by the 5th row from left to right. Enter the split cells in the order they are seen from the left (the upper triangle before the lower triangle).

Time Standards (highlight to view): Grandmaster = 2:00, Master = 2:40, Expert = 5:20

Solution: PDF

Note: Follow this link for other classic Skyscrapers and this link for variations on Skyscrapers puzzles. If you are new to this puzzle type, here are our easiest Skyscrapers to get started on.

PDF

or solve online (using our beta test of Penpa-Edit tools; use tab to alternate between Sudoku = big digits and Number candidate = small entries in the corners of cells.)

Theme: Equal Distribution and Symmetry of Clue Numbers

Author/Opus: This is the 2nd puzzle from guest contributor Roland Voigt.

Rules: Standard Skyscrapers rules. Also, some cells have been split into triangles, each of which must be filled with a number. In this puzzle, the numbers 1-5 must be placed in each row and column.

(The split cells are viewed in the order they are seen from a given direction, so the upper triangles are seen first from the left/top sides and the bottom triangles are seen first from the right/bottom sides.)

Answer String: Enter the 1st row from left to right, followed by a comma, followed by the 3rd row from left to right. Enter the split cells in the order they are seen from the left (the upper triangle before the lower triangle).

Time Standards (highlight to view): Grandmaster = 0:40, Master = 1:15, Expert = 2:30

Solution: PDF

Note: Follow this link for other classic Skyscrapers and this link for variations on Skyscrapers puzzles. If you are new to this puzzle type, here are our easiest Skyscrapers to get started on.

PDF

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

Theme: Going Up?

Author/Opus: This is the 171st puzzle from Thomas Snyder, aka Dr. Sudoku.

Rules: Variant of Skyscrapers rules. The numbers outside the grid represent the sum of the buildings seen in that row or column. For example, if a row is 12534, the clue from the left would be an 8 (1+2+5) and from the right would be a 9 (4+5).

Answer String: Enter the 3rd row from left to right, followed by a comma, followed by the 7th row from left to right.

Time Standards (highlight to view): Grandmaster = 3:15, Master = 4:30, Expert = 9:00

Solution: PDF

Note: Follow this link for classic Skyscrapers puzzles and this link for variations on Skyscrapers puzzles. If you are new to this puzzle type, here are our easiest Skyscrapers Puzzles to get started on.

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

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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)

Theme: Nine High

Rules: Variant of Skyscrapers rules. The numbers outside the grid represent the sum of the buildings seen in that row or column. For example, if a row is 12534, the clue from the left would be an 8 (1+2+5) and from the right would be a 9 (4+5).

Answer String: Enter the 2nd row from left to right, followed by a comma, followed by the 5th row from left to right.

Time Standards (highlight to view): Grandmaster = 1:00, Master = 2:15, Expert = 4:30

Solution: PDF

PDF

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

Theme: Clue Symmetry and Logic

Rules: Variation of Skyscrapers rules. Place digits 1-6 into the grid so that no digit is repeated within a row or column. Digits outside the grid indicate the number of buildings that can be seen from the corresponding direction. The buildings form two-digit numbers and the relations between some numbers are shown with a greater than/less than sign.

Or, see here.

Answer String: Enter the 3rd row from left to right, followed by a comma, followed by the 4th column from top to bottom.

Time Standards (highlight to view): Grandmaster = 5:15, Master = 7:30, Expert = 15:00

Solution: PDF

PDF

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

Theme: Clue Symmetry and Logic

Rules: Variation of Skyscrapers rules. Place digits 1-6 into the grid so that no digit is repeated within a row or column. Digits outside the grid indicate the number of buildings that can be seen from the corresponding direction. The buildings form two-digit numbers and the relations between some numbers are shown with a greater than/less than sign.

Or, see here.

Answer String: Enter the 2nd row from left to right, followed by a comma, followed by the 4th row from left to right.

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

Solution: PDF