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From: Udit Gangwani <uditg22@gmail.com>
Newsgroups: comp.programming
Subject: Re: double hashing
Date: Fri, 6 Apr 2012 03:34:08 -0700 (PDT)
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On Tuesday, 3 April 2012 01:19:06 UTC+5:30, Joe keane  wrote:
> question
> 
> We some have 'docs' that can be 'contracted' or 'expanded'.
> 
> They sometimes change from contracted to expanded and vice versa.
> 
> They each have a 'key' that's unique [and doesn't change when they
> change state].
> 
> struct condocinfo { ... };
> struct expdocinfo { ... };
> 
> The info for an expanded doc is a superset of the info for a contracted doc.
> [e.g., pointers to more structures].
> 
> Lookup by key.
> 
> Scheme 1
> 
> We keep a hash table for all docs that contains the info for contracted
> docs.  We keep a hash table for only expanded docs that contains the
> info for expanded docs that's not in the first one.
> 
> Scheme 2
> 
> We keep a hash table for only contracted docs that contains the info for
> contracted docs.  We keep a hash table for only expanded docs that
> contains the info for expanded docs.
> 
> Time?  Space?
> 
> [it's for an old project so it's academic]



On Tuesday, 3 April 2012 01:19:06 UTC+5:30, Joe keane  wrote:
> question
> 
> We some have 'docs' that can be 'contracted' or 'expanded'.
> 
> They sometimes change from contracted to expanded and vice versa.
> 
> They each have a 'key' that's unique [and doesn't change when they
> change state].
> 
> struct condocinfo { ... };
> struct expdocinfo { ... };
> 
> The info for an expanded doc is a superset of the info for a contracted doc.
> [e.g., pointers to more structures].
> 
> Lookup by key.
> 
> Scheme 1
> 
> We keep a hash table for all docs that contains the info for contracted
> docs.  We keep a hash table for only expanded docs that contains the
> info for expanded docs that's not in the first one.
> 
> Scheme 2
> 
> We keep a hash table for only contracted docs that contains the info for
> contracted docs.  We keep a hash table for only expanded docs that
> contains the info for expanded docs.
> 
> Time?  Space?
> 
> [it's for an old project so it's academic]

Since contracted info is a subset of expanded doc, and if the processing of contracted info from expanded info is order of constant then just maintain a single structure "struct expdocinfo { ... };" and a single Hash Table for it. 

Else
Keep a structure docInfo and keep both condocinfo{} and expdocinfo{} inside it and maintain a single Hash table with the value as a pointer to the docInfo object;

struct docInfo
{
   struct expdocinfo{} expDocInfoObj;
   struct condocinfo{} conDocInfoObj;
};