GridWits
Hard tier Technique 12 of 21 Smart Hint: Skyscrapers and Skyscrapers+

X-Wing

A height's only two candidate cells line up in the same two columns (or rows) across two rows (or columns) — eliminate it everywhere else in those columns or rows.

How it works

  1. 1Follow height 3. In row 1 it fits in only two cells, and in row 3 it fits in only two — and both rows point at the SAME two columns.
  2. 2The four tinted cells make a rectangle. Whichever corner row 1's 3 takes, row 3 is pushed to the opposite corner: the two 3s always end up one per column.
  3. 3So both of those columns already have their 3 accounted for by these two rows.
  4. 4Strike 3 from every other cell in the two columns. The rows themselves gain nothing — a fish pays out sideways, in the lines it crosses.
2 3 3 4 1 3 4 2 3 5 1 3 3 5 3 4 5 1 2 3 1 2 3 5 1 3 4 5
  • Height ruled out
  • Relationship — The arrow shows which cells support the deduction.
  • Conclusion — The final arrow lands beside the proved or ruled-out height.
Next in the ladder Naked Quad →

Four cells in a row or column whose candidates combine to exactly four heights — eliminate those heights elsewhere in the line.