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// -*- C++ -*-
// Copyright (C) 2005-2016 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library. This library is free
// software; you can redistribute it and/or modify it under the terms
// of the GNU General Public License as published by the Free Software
// Foundation; either version 3, or (at your option) any later
// version.
// This library is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// General Public License for more details.
// You should have received a copy of the GNU General Public License
// along with this library; see the file COPYING3. If not see
// <http://www.gnu.org/licenses/>.
// Copyright (C) 2004 Ami Tavory and Vladimir Dreizin, IBM-HRL.
// Permission to use, copy, modify, sell, and distribute this software
// is hereby granted without fee, provided that the above copyright
// notice appears in all copies, and that both that copyright notice
// and this permission notice appear in supporting documentation. None
// of the above authors, nor IBM Haifa Research Laboratories, make any
// representation about the suitability of this software for any
// purpose. It is provided "as is" without express or implied
// warranty.
/**
* @file store_hash_example.cpp
* An example showing how to store hash-values with
* each entry in a hash-based container.
*/
/**
* This example shows how to configure a hash-based container to store
* the hash value of each key along with each entry. This technique
* is useful for complex keys (e.g., strings in this example), since
* it lowers the cost of collisions. For simpler types (e.g., integers),
* where the cost of comparing keys is of the same order as the cost
* of comparing hash values, this technique adds unnecessary overhead.
*/
#include <functional>
#include <string>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/hash_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
// A string hash functor.
struct string_hash : public unary_function<string, size_t>
{
inline size_t
operator()(string str) const
{
string::const_iterator b = str.begin();
string::const_iterator e = str.end();
size_t hash = 0;
while (b != e)
{
hash *= 5;
hash += static_cast<size_t>(*b);
++b;
}
return hash;
}
};
int main()
{
// A collision-chaining hash table mapping strings to ints.
typedef
cc_hash_table<
string,
int,
string_hash,
equal_to<string>,
direct_mask_range_hashing<>,
hash_standard_resize_policy<>,
true>
map_t;
map_t h;
// Use regularly.
h["Hello, "] = 0;
h["world"] = 1;
return 0;
}
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