Re: Should I implement this using string hash or multimap..
Jonay Aloat <jonhat@comcast.net> wrote:
I need to implement the following. Shoul I use multimap or write a string
hash class? ie
Brand Product
==========================
Samson Television
Samsung Television
Samsung VCR
Samsung DVD Player
Samsunk Television
The brand is the key and the product is the data.
If I use multimap, then I can implement it using something like this
typedef std::multimap<string, string> mmap;
typedef std::multimap<string, string>::iterator mapIter;
mmap product_map;
product_map.insert( pair<string, string> string a(Samsung), string
b(Television));
..
..
..
To find the product in brand, all I have to do is iterate using lower and
upper bound.
mapIter lowerB = product_map.lower_bound("Samsung");
mapIter upperB = product_map.upper_bound("Samsung");
for (lowerB; lowerB != upperB; ++lowerB) {
string p = (*lowerB).second;
if ( strcmp (p.c_str(), "VCR") == 0 ) ) {
//do something
} else {
//do something
}
}
Assume that I have a lot of data. Is this implementation efficient? I know
using string as the key is not a good idea. Is there a better way to do
this? Is the performance better using hash? How do I implent the hash
function.
How big is a lot??? 4066 of each? 1 meg of each ??
Asunning the # of companies no_companies < = numeric_limits<unsigned
short> ::max() and the no_products <= numeric_limits<unsigned
short>::max() typically 32k or larger.
and sizeof(unsigned short) *2 <= sizeof(unsigned long) then a simple
shift and or provides a hash.
generically
unsiged long hash(std::pair<unsigned short,unsigned short> x)
{
unsigend long k = x.first;
return k << (sizeof(unsiged short)*CHAR_BIT) | x.second;
}
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