Question

I have two space separated strings… (the X doesn’t mean the same symbol)

st1 = "abc def kok...."
st2 = "kok bbr def ffe ...."

i would like to construct an intersection string as follows:
common = "kok def"

what is the efficient way to do so in c++?

Thanks

Answer 1

Use std::set_intersection

Sample program:

I’m assuming you’ve tokenized your strings already (this solution seems easy to implement).

// Data
std::vector<string> a,b;
a.push_back("abc");b.push_back("kok");
a.push_back("def");b.push_back("bbr");
a.push_back("kok");b.push_back("def");
a.push_back("foo");b.push_back("ffe");

// Allocate space for intersection
std::vector<string> v(a.size()+b.size());

// Sort as required by set_intersection
std::sort(a.begin(),a.end());
std::sort(b.begin(),b.end());
// Compute
std::vector<string>::iterator it = std::set_intersection(a.begin(),a.end(),b.begin(),b.end(),v.begin());

// Display
v.erase(it,v.end());
for(std::vector<string>::iterator it = v.begin();it < v.end(); ++it) std::cout<<*it<<std::endl;

Complexity should be O(n log n) in the number of tokens (or sub-strings).