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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排序算法
｜
67
排序算法
for (i = n/2-1; i>=0; i--) {
heapify (ar, cmp, i, n);
}
}
void sortPointers (void **ar, int n,
int(*cmp)(const void *, const void *)) {
int i;
buildHeap (ar, cmp, n);
for (i = n-1; i >= 1; i--) {
void *tmp;
tmp = ar[0];
ar[0] = ar[i];
ar[i] = tmp;
heapify (ar, cmp, 0, i);
}
}
4.4.3 算法分析
堆排序
的核心操作是
heapify
。在
buildHeap
中
，这个函数将会被调用
⎣
(
n/
2)
⎦
－
1
次，
在实际排序中，它也会被调用
n
－
1
次，因此总共调用了
⎣
(3
*n/
2)
⎦
－
2
次。由于
外形性质
，
堆的深度总是为
⎣
log
n
⎦
，其 中
n
为堆中元素的个数。如你所见，这是一个递归的操作，
且递归的调用次数在堆被校正或者到达堆的底部之前不多于
log
n
。尽管如此，一旦堆被
校正之后，
heapify
会提早结束。结果显示，整个过程需要的比较次数不多于
2
*
n
（
Cormen
等，
2009
），这意味着
buildHeap
的执行时间是
O(
n
)
。
4.4.4 衍生算法
代码库中包含了
堆排序
的非递归实现，表
4-4
列出了对两种实现执行
1000
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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.