Sunday, February 3, 2013

use STL Map to emulate a Set

Q1: is it practical to use a STL Map to emulate the Set class-template, at comparable efficiency?

We know a Map stores PAIRs in a red-black tree. Can we just put an empty thing in the PAIR.second field?

Q2: how small can the "PAIR.second" footprint be? 0 byte? 1 byte?
%%A: i don't think it can be 0 byte. sizeof(PAIR) is known when you specialize the PAIR template with T1 and T2. sizeof(PAIR) depends on sizeof(T1) + sizeof(T2). Compiler needs to know sizeof(PAIR) in order to allocate memory to a new PAIR object.

Q3: is there any type T2 such that sizeof(T2) == 0?
%%A: I don't know any.

Q4: we know java HashSet is implemented using HashMap physically. Is that different from C++?

Q5: java TreeSet.java source code shows a physical implementation using a map. Is that different from STL?

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