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// -*- C++ -*-

// Copyright (C) 2005, 2006, 2009 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;

}