Skyscraper

Hard

Two conjugate pairs in different columns share one row; cells seeing both free ends can have the digit eliminated.

How It Works

For a given digit, two columns each have a conjugate pair. If one end of each pair shares the same row, the other two ends act like a Naked Pair — any cell seeing both free ends can have the digit eliminated.

Part of the "Turbot Fish" family, using basic chain logic.

Example

23	1	4	2	36	9	4	2	7
9	2	5	3	4	7	3	1	5
6	9	1	4	2	8	5	7	6
379	1	2	5	179	4	6	8	3
38	6	9	7	35	8	2	4	9
146	5	4	8	268	5	9	7	8
35	7	6	4	37	6	8	5	4
289	6	5	1	248	9	6	5	7
146	2	3	6	145	7	5	8	9

Key cells of the techniqueCells where elimination is appliedCandidate to be placedEliminated candidate (crossed out)

Digit 3: Column 2 has conjugate pair at R1,R6; Column 8 at R1,R4. Row 1 is shared → Eliminate 3 from cells seeing both R6C2 and R4C8.

Practice with a Real Puzzle

This 9×9 puzzle is solver-verified to require this technique on its solution path.

Medium26 givens

23	1	4	2	36	9	4	2	7
9	2	5	3	4	7	3	1	5
6	9	1	4	2	8	5	7	6
379	1	2	5	179	4	6	8	3
38	6	9	7	35	8	2	4	9
146	5	4	8	268	5	9	7	8
35	7	6	4	37	6	8	5	4
289	6	5	1	248	9	6	5	7
146	2	3	6	145	7	5	8	9

23	1	4	2	36	9	4	2	7
9	2	5	3	4	7	3	1	5
6	9	1	4	2	8	5	7	6
379	1	2	5	179	4	6	8	3
38	6	9	7	35	8	2	4	9
146	5	4	8	268	5	9	7	8
35	7	6	4	37	6	8	5	4
289	6	5	1	248	9	6	5	7
146	2	3	6	145	7	5	8	9

23	1	4	2	36	9	4	2	7
9	2	5	3	4	7	3	1	5
6	9	1	4	2	8	5	7	6
379	1	2	5	179	4	6	8	3
38	6	9	7	35	8	2	4	9
146	5	4	8	268	5	9	7	8
35	7	6	4	37	6	8	5	4
289	6	5	1	248	9	6	5	7
146	2	3	6	145	7	5	8	9