Skyscraper and 2-String Kite

Expert

Skyscraper and 2-String Kite use two lines where a digit has only two places each, joined at one end. One of the two far ends must then hold the digit, so any cell that sees both far ends can’t.

Skyscraper

Take two rows (or two columns) where a digit has exactly two places each. If one place in each row sees the other, the two can’t both be the digit, so at least one of the other two places is. Those are the tops of the skyscraper: any cell that sees both tops loses the digit.

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Only the notes for 2 are shown. In rows A and E, a 2 fits in two places each. A5 and E5 see each other (dashed line), so they can’t both be a 2: A1 or E3 must be. C3 sees both, so it can’t be a 2.

2-String Kite

The same idea with one row and one column, joined inside a box. Where they meet, the two places see each other, so one of the far ends holds the digit.

222222222222214739843171454897152633712649652389492887696981A2B3C4D5E6F7G8H9I
Only the notes for 2 are shown. In row B and column 2, a 2 fits in two places each. B1 and C2 see each other (dashed line), so they can’t both be a 2: B8 or H2 must be. H8 sees both, so it can’t be a 2.

How to spot them

  • Show one digit’s notes and look for lines with exactly two of them: each is a strong link, where one of the two must be the digit.
  • Two such lines with ends that see each other make the pattern. The cells to clear are where the far ends’ rows, columns and boxes cross.
  • Both are the shortest chains there are: three links on one digit.

Try it on a real puzzle

Expert puzzles in Sudoku Knockout need techniques like this one, and never a guess. When you’re stuck, a hint shows you the step.

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