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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搜索算法
｜
99
搜索算法
5.3.2 使用环境
假设有一个数组，它包含了
213 557
个英语单词（可以在本书的代码库中找到）。在
二
分搜索
中我们得知，使用二分搜索需要进行大约
18
次字符串比较（因为
log(213557) =
17.70
）。而使用
散列搜索
，字符串比较的次数只与链表的长度相关，与数组的长度无关。
我们首先需要定义一个
散列
函数，旨在生成尽可能多的值。在过去的几十年间，科学家
们花费了大量的心血在散列计算上，并且发表了大量的论文来设计和描述高效的散列函
数，这些散列函数的使用范围已经不仅仅局限于搜索查找，举个例子，某些特殊的散列
函数可以在密码学方面大展宏图。对于搜索来说，散列函数应能产生均匀的散列值分布，
并能够在较快时间（以机器周期计）内快速计算出结果。
散列搜索算法小结
最好情况和平均情况：
O
(1)
最坏情况：
O
(
n
)
loadTable (size, C)
H = new array of given size
foreach e in C do
h = hash(e)
if H[h] is empty then
❶
H[h] = new Linked List
add e to H[h]
return A
end
search (H, t)
h = hash(t)
list = H[h]
if list is empty then
return false
if list contains t then
❷
return
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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.