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// -*- C++ -*-
// Copyright (C) 2005-2019 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 basic_multimap_example.cpp
* A basic example showing how to use multimaps.
*/
/**
* This example shows how to use "multimaps" in the context of a simple
* bank account application. Each customer holds a bank account
* (or more than one) which holds some balance.
*/
#include <iostream>
#include <string>
#include <cassert>
#include <ext/pb_ds/assoc_container.hpp>
using namespace std;
using namespace __gnu_pbds;
// A simple hash functor.
// hash could serve instead of this functor, but it is not yet
// standard everywhere.
struct string_hash : public unary_function<string, size_t>
{
inline size_t
operator()(const string& r_s) const
{
size_t ret = 0;
string::const_iterator b = r_s.begin();
string::const_iterator e = r_s.end();
while (b != e)
{
ret *= 5;
ret += static_cast<size_t>(*(b++));
}
return ret;
}
};
int main()
{
// Each customer is identified by a string.
typedef string customer;
// Each account is identified by an unsigned long.
typedef unsigned long account_id;
// The balance in the account is a floating point.
typedef float balance_t;
/*
* This is the data structure type used for storing information
* about accounts. In this case the primary key is the customer,
* and the secondary key is the account id.
*
* A hash-based container maps each customer to a list-based
* container that maps each account to the balance it holds.
*
* Note that we could use any combination of primary and secondary
* associative-containers. In this case we choose a hash-based
* container for the primary keys, since we do not need to store
* customers in a sorted order; we choos a list-based container for
* the secondary keys, since we expect that the average number of
* accounts per customer will be small.
*/
typedef
cc_hash_table<
customer,
list_update<
account_id,
balance_t>,
string_hash>
accounts_t;
// This object will hold all information.
accounts_t acc;
// Customer "a" opens empty account 12.
acc["a"][12] = 0;
// Customer "a" deposits 45 into account 12.
acc["a"][12] += 45;
// Customer "b" opens account 13 with balance 12.3.
acc["b"][13] = 12.3;
// Customer "c" opens empty account 14.
acc["c"][14] = 0;
// Customer "a" opens account 160 with balance 142.
// Note that "a" already holds account 12.
acc["a"][160] = 142;
// Verify the number of accounts that "a" holds.
accounts_t::point_const_iterator it = acc.find("a");
assert(it != acc.end());
assert(it->second.size() == 2);
// The beginning of the month has arrived. We need to give a 3%
// interest to all accounts with a positive balance.
// First we loop over all customers.
accounts_t::iterator cust_it;
for (cust_it = acc.begin(); cust_it != acc.end(); ++cust_it)
{
// For each customer, we loop over the customer's accounts.
accounts_t::mapped_type::iterator it;
for (it = cust_it->second.begin(); it != cust_it->second.end(); ++it)
if (it->second > 0)
it->second *= 1.03;
}
// Customer "a" closes all accounts.
acc.erase("a");
// The bank now has only 2 customers.
assert(acc.size() == 2);
return 0;
}
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