J*****n
发帖数: 4859 | 1 今天一个同事跟我说他的困惑
他有一个三维数组存成vector of vector of vector（assume i,j,k）
然后他对其中的k，进行排序，然后使用lower_bound function去查找相关的iter，重
复了2million time。
结果他发现这个的速度很慢，还不如他自己写的binary search。（慢了一倍）
我想了半天，也没想出个名堂。
照理说stl的那些基本container和function都是优化的很好的，如果要慢，也不会慢一
倍那么多。
求高手指点一二，谢谢。 |
e*****r
发帖数: 379 | |
J*****n
发帖数: 4859 | 3
No, I think what he did likes:
lower_bound(p[i][j].begin(), p[i][j].end(), some double number)
I think in this case, memory of k is contingous and search range is just
from 0 to k - 1.
【在 e*****r 的大作中提到】
: O(n^3)
: O(log2(n^3))...
|
p***o
发帖数: 1252 | 4 Sounds like you are using the checked iterators.
Read your STL manual/source code to see if that could be the case.
Also you can compare asm listings to determine why.
【在 J*****n 的大作中提到】
:
: No, I think what he did likes:
: lower_bound(p[i][j].begin(), p[i][j].end(), some double number)
: I think in this case, memory of k is contingous and search range is just
: from 0 to k - 1.
|
J*****n
发帖数: 4859 | 5
We use VS 2010 here.
What's your suggestion about improvment?
【在 p***o 的大作中提到】
: Sounds like you are using the checked iterators.
: Read your STL manual/source code to see if that could be the case.
: Also you can compare asm listings to determine why.
|
p***o
发帖数: 1252 | 6 #define _SECURE_SCL 0
【在 J*****n 的大作中提到】
:
: We use VS 2010 here.
: What's your suggestion about improvment?
|
J*****n
发帖数: 4859 | 7
Thank you.
【在 p***o 的大作中提到】
: #define _SECURE_SCL 0
|
e*****r
发帖数: 379 | 8 for small scripts, it is OK to turn it off -- trouble mixing between classes
and modules for checked/unchecked
【在 p***o 的大作中提到】
: #define _SECURE_SCL 0
|
J*****n
发帖数: 4859 | 9
classes
BTW, should I put it in the main function code or the sub code where we need
it?
【在 e*****r 的大作中提到】
: for small scripts, it is OK to turn it off -- trouble mixing between classes
: and modules for checked/unchecked
|
