2-String Kite
A 2-String Kite is a single-digit pattern made of one row and one column in which a digit has exactly two candidate cells each. One cell of the row and one cell of the column lie in the same box, so at most one of them holds the digit. Therefore at least one of the two other cells, the ends of the kite, holds it, and the digit can be removed from every cell that sees both ends. Like the Skyscraper, it is a form of Turbot Fish, and it is an Expert technique in Bare Sudoku.
When to use it
When the Skyscraper and the patterns before it find nothing. 2-String Kites are less common than Skyscrapers. Look for them when a digit is down to two candidates in a row and two in a column, with one candidate of each in the same box. They need complete notes for that digit.
How to spot it
Pick a digit and find a row where it has exactly two candidate cells and a column where it has exactly two, with no cell in common. If one cell of the row and one cell of the column share a box, the two remaining cells are the ends of the kite. Then look at the cells that see both ends; usually there is just one, in the row of one end and the column of the other. In the game, tap the digit key: the row and the column each show two highlighted notes.
Example
| c1 | c2 | c3 | c4 | c5 | c6 | c7 | c8 | c9 | |
|---|---|---|---|---|---|---|---|---|---|
| r1 | 124 | 7 | 12468 | 146 | 5 | 1468 | 3 | 12689 | 689 |
| r2 | 3 | 9 | 1468 | 7 | 2 | 1468 | 168 | 168 | 5 |
| r3 | 12 | 18 | 5 | 16 | 9 | 3 | 12678 | 12678 | 4 |
| r4 | 145 | 6 | 9 | 145 | 3 | 14 | 78 | 78 | 2 |
| r5 | 7 | 2 | 3 | 8 | 6 | 9 | 5 | 4 | 1 |
| r6 | 8 | 145 | 14 | 1245 | 7 | 1245 | 69 | 69 | 3 |
| r7 | 9 | 15 | 12 | 3 | 8 | 256 | 4 | 126 | 7 |
| r8 | 6 | 3 | 128 | 29 | 4 | 7 | 1289 | 5 | 89 |
| r9 | 245 | 458 | 7 | 2569 | 1 | 256 | 2689 | 3 | 689 |
Bold digits are given, blue digits were placed while solving, small digits are candidates. Highlighted cells form the pattern, crossed-out candidates are removed, and a circled candidate is the digit to place.
- Digit 5 has exactly two candidate cells in row 7, r7c2 and r7c6, and exactly two in column 1, r9c1 and r4c1.
- r7c2 and r9c1 are both in box 7, so at most one of them can be 5.
- If r7c2 is not 5, row 7 must put its 5 in r7c6. If r9c1 is not 5, column 1 must put its 5 in r4c1. At least one of the two box cells is not 5, so r7c6 or r4c1 is 5.
- A cell that sees both r7c6 and r4c1 can never be 5. Remove 5 from r4c6.
Common mistakes
- Using a row or a column with three candidate cells for the digit. Both strings must have exactly two.
- Joining the strings through cells in different boxes. The pattern only works because the two inner cells share a box, so they cannot both hold the digit.
- Removing the digit from the box that joins the strings, or from cells that see only one end. Only cells that see both ends lose the digit.
In Bare Sudoku
Needed from level: Expert
In the game, the hint says: 2-String Kite
Frequently asked questions
What is a 2-String Kite in Sudoku?
A pattern of one digit with exactly two candidate cells in a row and exactly two in a column. One cell of the row and one of the column share a box, so at least one of the other two cells holds the digit, and it is removed from every cell that sees both of them.
Why is it called a 2-String Kite?
The row and the column are the two strings, each holding exactly two candidates, and the box where they meet ties them together. Drawn on the grid, the two strings and the box look like a kite.
Is a 2-String Kite a Turbot Fish?
Yes. Like the Skyscraper, it joins two units in which the digit has exactly two candidates through two cells that see each other. In the kite the units are a row and a column, and the two joined cells share a box.
How is a 2-String Kite different from a Skyscraper?
A Skyscraper uses two parallel lines, two rows or two columns, joined in a shared column or row. A 2-String Kite uses one row and one column joined in a box. The reasoning and the eliminations work the same way.
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