August 2017
Intermediate to advanced
360 pages
8h 35m
Chinese
Content preview from 算法技术手册（原书第2 版）
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238
｜
第
9
章
join upper and lower (remove duplicate end points)
❻
return computed hull
❶
排序是本算法中费用最大的部分。
❷
假设这两个点属于上凸包。
❸
左拐的线条意味着凸包上最后三个点并没有组成一个凸角。
❹
中间的点不满足条件，需要删除。
❺
用类似的办法计算下凸包。
❻
把这两个凸包
合并在一起。
图
9-3
展示了
凸包扫描
算法是如何构建上凸包的。可以看到，在整个过程中，该算法在
从左到右访问
P
中每个点的过程中，会不断地做出一些错误的决定。但是算法会不断地
检查并且删除掉三个点中不满足条件的中点，以纠正之前的错误。
图 9-3：增量构建上凸包
9.3.1 输入 / 输出
输入是平面上的二维点集
P
。
凸包扫描
算法会计算出一个有序表
L
，包含顺时针组成凸包的
h
个顶点。即点
L
0
，
L
1
，…，
L
h-
1
组成的多边形，
h
是点的数目，这个凸包有
h
条边：
<
L
0
，
L
1
>
，
<
L
1
，
L
2
>
，…，
<
L
h
-1
，
L
0
>
。
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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.
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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.