September 2014
Intermediate to advanced
336 pages
7h 53m
Japanese
Content preview from アンダースタンディング コンピュテーション ―単純な機械から不可能なプログラムまで
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4.4
どれだけ能力があるか
133
図4-7
4.4
どれだけ能力があるか
この章では、計算能力について、新たに2つのレベルを見てきました。DPDAはDFAとNFAよりも
能力が高く、NPDAはさらに能力が高いことがわかりました。プッシュダウン・オートマトンはスタッ
クにアクセスすることで、有限オートマトンよりも少しだけ高い能力と機能を得たようです。
スタックを持つことによって、PDAは回文やバランスのとれた括弧のような、有限オートマトンが認
識できない言語を認識できるようになりました。スタックが提供する無限のストレージのおかげで、
PDAは計算中に任意の情報を覚えておき、あとでそれを参照することができます。
有限オートマトンと違って、PDAは入力を読まずに無限にループすることができます。このことは
具体的に役に立たないとしても、気になるところです。DFAは入力文字を消費することでしか状態を
変えられません。NFAは自由移動によって自発的に状態を変えることができますが、最終的に開始し
134
4
章 能力を高める
た場所に戻るまで、有限回しか変えられません。これに対して、PDAは1つの状態にとどまり、一度
も同じ構成を繰り返すことなく、永久に文字をスタックにプッシュし続けることができます。
プッシュダウン・オー
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.