Sudoku technique guide

Skyscraper Sudoku Technique

A Skyscraper uses two strong links for one candidate to remove a candidate seen by both tops. This guide explains the idea in plain English, when to look for it, and the common mistake to avoid.

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At a glance

Difficulty

Hard

This is where Skyscraper normally sits in a human solving path.

Family

Single-digit chain techniques

It belongs to the single-digit chain techniques group of Sudoku logic.

Main action

Usually remove candidates

Most technique moves reduce notes first. That often reveals a simpler placement afterwards.

What is Skyscraper?

A Skyscraper uses two strong links for one candidate to remove a candidate seen by both tops.

The important thing is that this is logic, not guessing. You are using the current candidates to prove that a number must either go in one place, or cannot stay in another place.

In SudoSketch, this technique is designed to work with notes and Coach highlighting, so the key cells and removal cells can be shown clearly.

How Skyscraper works

Focus on one candidate.
Find two rows or columns where the candidate appears exactly twice.
If one side lines up, at least one opposite end must be true, removing candidates that see both ends.

When to look for it

Look for Skyscraper after easier moves have stopped working. First check for naked singles, hidden singles, locked candidates and simple pairs. If those do not move the puzzle forward, this technique may be worth checking.

For learning, do not try to scan for every advanced technique at once. Pick one method, understand the shape, and practise spotting that one pattern.

Common mistake

The elimination cell must see both tower tops, not just one.

If you are unsure, rebuild the candidates first. Bad notes create bad logic, and Sudoku will absolutely punish you for it like a tiny spreadsheet goblin.

Skyscraper FAQ

What is Skyscraper in Sudoku?