---
title: "Skyscraper: Sudoku Technique #17 | Sudoku Flow"
description: "Skyscraper: When two strong links on one number have floor ends that share a row or column, at least one roof end must hold it, and any cell seeing both roofs…"
url: https://sudokuflow.com/lessons/skyscraper/
language: en
---

[Sudoku technique lessons](https://sudokuflow.com/lessons/) / Skyscraper

Lesson 17

# Skyscraper

## The rule

When two strong links on one number have floor ends that share a row or column, at least one roof end must hold it, and any cell seeing both roofs loses that candidate.

## Step by step

1. In each of the two highlighted columns, 3 can only go in two cells (a strong link). The two cells marked (the floor) share one row. The two cells marked (the roof) stand in two different rows. This is a Skyscraper!
2. 3 must be in at least one of the two roof cells , so we can remove the candidate 3 from any other cell that sees both of them.

[Read the full lesson, with more examples →](https://sudoku.rubigogames.com/techniques/skyscraper.html)

In our app, when this technique is the next step, the hint names it and shows you why, step by step. No ads, free to download.

[App Store iPhone, iPad, Mac](https://apps.apple.com/app/apple-store/id6502922368?pt=125379530&ct=sudokuflow_cta&mt=8) [Google Play Android](https://play.google.com/store/apps/details?id=com.rubigogames.sudoku&referrer=utm_source%3Dsudokuflow%26utm_medium%3Dcta%26utm_campaign%3Dlesson)

## Try it on more boards

Each board is a real puzzle from our app, at a moment where Skyscraper applies. Find the step yourself, or tap Hint and the app's own hint walks you through it.

Skyscraper practice board:

```text
.  8  .  | 1  4* .  | 2  .  .
4  .  .  | .  7  .  | .  8  5
.  .  6  | 9  .  8* | .  .  .
---------+----------+---------
.  5* .  | 4  1* 9  | 3  6  7*
1  .  .  | .  6* .  | .  5  .
7  6* .  | .  3  .  | .  .  .
---------+----------+---------
.  .  .  | .  .  .  | .  4  1
3  .  .  | 6  9* 1  | 5  .  .
.  2  1* | .  8  4* | .  3  .
```
Digits marked * were filled in by a player; the others were printed with the puzzle.

![Sudoku app icon](https://sudokuflow.com/assets/app-icon.png)

## Want more boards like this?

We also make a Sudoku app for iPhone, iPad, Mac and Android. There are no ads in it at all, it works offline, and when you ask for a hint it shows you the technique instead of just filling in a number.

[App Store iPhone, iPad, Mac](https://apps.apple.com/app/apple-store/id6502922368?pt=125379530&ct=sudokuflow_web&mt=8) [Google Play Android](https://play.google.com/store/apps/details?id=com.rubigogames.sudoku&referrer=utm_source%3Dsudokuflow%26utm_medium%3Dweb%26utm_campaign%3Dsite)

Sudoku Flow is made by Rubigo Games, the developer of the Sudoku app recommended on this site.