December 2016
Intermediate to advanced
440 pages
9h 44m
Japanese
Content preview from アルゴリズムクイックリファレンス 第2版
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330
■
10
章 空間木構造
//
見つかれば小さいものを使う。
if (newResult != null) { return newResult; }
}
return result;
}
最近傍法
を理解する鍵は、最初に対象点が挿入されるであろう領域を見つけるこ
とにある。なぜなら、その領域が最近点を含む可能性が高いからである。次に、こ
の仮定を検証するために、根からこの領域へ再帰的に戻りながら、他の点が実際に
はより近くないかどうか（これは
k-d
木の長方形領域が任意の入力集合に基づいて
作られるので、簡単に起こりやすい）調べていく。非平衡
k-d
木では、この確認処
理のために全体コストが
O(n)
となるので、入力集合を適切に処理することが重要
だということを再認識できる。
例に挙げた解は性能向上の点で
2
つ改善している。まず、点を表現する「生の」
double
配列で比較が行われている。次に、
2
つの
d
次元の点の間の距離が、これま
で計算された最小距離より小さいかどうかは、
DimensionalNode
の
shorter
メソッ
ドで判定している。このメソッドは、ユークリッド距離の計算中にこれまで見つけ
た最小距離を超えることがわかった時点で抜け出す。
最初の
k-d
木が平衡している場合、再帰呼び出しで探索する際に、木の中の半分
の点を棄却するという利点がある。
2
つの再帰呼び出しが必要なときもあるが、計
算された最小距離が、節点の分割線をちょうど越える大きさのときだけである。そ
の場合には、最近点を見つけるため
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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.