The Two-String Kite Technique in Sudoku

What Is a Two-String Kite?

A Two-String Kite uses one strong link in a row and one strong link in a column for the same candidate. One endpoint from each strong link lies in the same block. The two opposite endpoints cannot both be false, so any cell that sees both of them cannot contain the candidate.

How to Identify the Pattern

1. Choose a candidate digit.
2. Find a row where it has exactly two positions.
3. Find a column where it also has exactly two positions.
4. Confirm that one endpoint from each pair shares a block.
5. Eliminate the digit from cells that see both opposite endpoints.

Candidate 5 forms a row strong link at R2C2-R2C8 and a column strong link at R3C3-R8C3. R2C2 and R3C3 share block 1. Therefore, at least one of the opposite endpoints R2C8 or R8C3 must be 5, and candidate 5 can be removed from R8C8.

Why the Elimination Is Valid

If R2C8 is false, R2C2 must be 5. That removes 5 from R3C3 in the shared block, forcing R8C3 to be 5. The reverse conclusion is immediate when R2C8 is true. In either case, R8C8 sees a true 5.

How Is It Different From Skyscraper?

Skyscraper usually uses two strong links of the same orientation. Two-String Kite combines a row link with a column link and joins them through a block.

What Are Common Two-String Kite Mistakes?

Both pairs must be genuine strong links for the same digit. The bridge endpoints must share one block, and the elimination cell must see both opposite endpoints.

A Practical Search Workflow

Filter one digit and mark rows and columns in which it appears exactly twice. Compare one row link with one column link and look for endpoints sharing a block. Only after confirming the bridge should you inspect the intersection seen by both outer endpoints.

Frequently Asked Questions

Must the two outer endpoints see each other?

No. They are normally separated. The target cell, not the endpoints, must see both.

Can the kite be rotated?

Yes. Orientation does not matter as long as the row link, column link, shared block, and visibility relationships remain valid.

Summary

Use one digit, one row link, one column link, and one block bridge. Missing any of these conditions invalidates the elimination.