optimization

问题 For small sets or maps, it's usually much faster to just use a sorted vector, instead of the tree-based set / map - especially for something like 5-10 elements. LLVM has some classes in that spirit, but no real adapter that would provide a std::map like interface backed up with a std::vector . Any (free) implementation of this out there? Edit : Thanks for all the alternative ideas, but I'm really interested in a vector based set/map. I do have specific cases where I tend to create huge

问题 Given n integers between [0,10000] as D 1 ,D 2 ...,D n , where there may be duplicates, and n can be huge: I want to find k distinct representative integers (for example k=5) between [0,10000] as R 1 ,R 2 ,...,R k , so the sum of errors of all the representative integers is minimized. The error of a representative integer is defined below: Assuming we have k representative integers in ascending order as {R 1 ,R 2 ...,R k }, the error of R i is : and i want to minimize the sum of errors of the

问题 Closed . This question is opinion-based. It is not currently accepting answers. Want to improve this question? Update the question so it can be answered with facts and citations by editing this post. Closed 3 years ago . I used both of these compilers in different projects. How they are different in terms of code processing and output generations? For example both gcc and clang has -O2 options for optimization. Are they operating the same way (high level) in terms of optimizing code? I did a

问题 I'm building a site with Jekyll for the first time. I'm loving it so far; my only problem is the exceedingly long build times. Right now, when I run jekyll build , it takes about 30 seconds to generate the site. 30 seconds might not seem like a lot, but at the moment, the entire site only has ONE post, 8 includes, 8 layouts, and 2 small plugins . I haven't abused liquid tags to my knowledge, and if I remove the plugins, it still takes just as long. When searching for an answer, all I can find

问题 I'm using the UIImagePickerController in my app. Has anyone used any optimization tricks for picture-taking latency? I don't need to store them to the library. I simply want to capture the pixel data and destroy the image object after making a calculation. Also, is there a way to hide the lens when it loads? (Worst case, I could mask the lens on camera startup and mask the frozen image upon saving/calculating.) EDIT: I've already set showsCameraControls = NO; . This hides the lens effect

问题 After searching the net I came to know that the bit-wise version of the sieve of eratosthenes is pretty efficient. The problem is I am unable to understand the math/method it is using. The version that I have been busy with looks like this: #define MAX 100000000 #define LIM 10000 unsigned flag[MAX>>6]={0}; #define ifc(n) (flag[n>>6]&(1<<((n>>1)&31))) //LINE 1 #define isc(n) (flag[n>>6]|=(1<<((n>>1)&31))) //LINE 2 void sieve() { unsigned i, j, k; for(i=3; i<LIM; i+=2) if(!ifc(i)) for(j=i*i, k

问题 In PHP we normally do coding without considering what the server is capable of. Now a days even PCs have multiple cores and process 64 bit data also. As far as I know the PHP engine itself is optimised to take advantage of multiple cores. How can we programmers can optimize further the code to take advantage of multiple cores. In other words I want to know the techniques that will teach me to write code which will be more likely to be considered by php engine to process parallely. I'm not

问题 I was attempting to create a faster version of String.equals() method and started by simply copying it. The result I found was quite confusing. When I ran the copy pasted version, timed it and compared it against the JVM one, the JVM version was faster. The difference ranged from 6x to 34x faster! Simply put, the longer the string, larger is the difference. boolean equals(final char a[], final char b[]) { int n = a.length; int i = 0; while (n-- != 0) { if (a[i] != b[i]) return false; i++; }

问题 I was attempting to create a faster version of String.equals() method and started by simply copying it. The result I found was quite confusing. When I ran the copy pasted version, timed it and compared it against the JVM one, the JVM version was faster. The difference ranged from 6x to 34x faster! Simply put, the longer the string, larger is the difference. boolean equals(final char a[], final char b[]) { int n = a.length; int i = 0; while (n-- != 0) { if (a[i] != b[i]) return false; i++; }

问题 I'm aware of the fact that assigning an rvalue to a const lvalue reference extends the temporaries lifetime until the end of the scope. However, it is not clear to me when to use this and when to rely on the return value optimization. LargeObject lofactory( ... ) { // construct a LargeObject in a way that is OK for RVO/NRVO } int main() { const LargeObject& mylo1 = lofactory( ... ); // using const& LargeObject mylo2 = lofactory( ... ); // same as above because of RVO/NRVO ? } According to