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It's likely been installed on more than a million devices too.

Even on more than a dozen devices when you think about it.

At least two!

Correct. They say a billion later on in the article. That's a typo

"Microsoft Solitaire has likely been installed on more than one device."

An optimal implementation of Dijkstra's algorithm i O(nⁿ) in the number of vertices.

Just like Doom as well