| // -*- C++ -*- |
| |
| // Copyright (C) 2005, 2006 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 2, 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 COPYING. If not, write to |
| // the Free Software Foundation, 59 Temple Place - Suite 330, Boston, |
| // MA 02111-1307, USA. |
| |
| // As a special exception, you may use this file as part of a free |
| // software library without restriction. Specifically, if other files |
| // instantiate templates or use macros or inline functions from this |
| // file, or you compile this file and link it with other files to |
| // produce an executable, this file does not by itself cause the |
| // resulting executable to be covered by the GNU General Public |
| // License. This exception does not however invalidate any other |
| // reasons why the executable file might be covered by the GNU General |
| // Public License. |
| |
| // 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 priority_queue_xref_example.cpp |
| * A basic example showing how to cross-reference priority queues and other |
| * containers for erase. |
| */ |
| |
| /** |
| * This example shows how to cross-reference priority queues |
| * and other containers. I.e., using an associative container to |
| * map keys to entries in a priority queue, and using the priority |
| * queue to map entries to the associative container. The combination |
| * can be used for fast operations involving both priorities and |
| * arbitrary keys. |
| * |
| * The most useful examples of this technique are usually from the |
| * field of graph algorithms (where erasing or modifying an arbitrary |
| * entry of a priority queue is sometimes necessary), but a full-blown |
| * example would be too long. Instead, this example shows a very simple |
| * version of Dijkstra's |
| */ |
| |
| #include <iostream> |
| #include <cassert> |
| #include <ext/pb_ds/priority_queue.hpp> |
| #include <ext/pb_ds/assoc_container.hpp> |
| |
| using namespace std; |
| using namespace pb_ds; |
| using namespace pb_ds; |
| |
| // A priority queue of integers, which supports fast pushes, |
| // duplicated-int avoidance, and arbitrary-int erases. |
| class mapped_priority_queue |
| { |
| public: |
| |
| // Pushes an int into the container. If the key is already in, this |
| // is a no-op. |
| void |
| push(const int& r_str); |
| |
| // Returns a const reference to the largest int in the container. |
| const int |
| top() const |
| { |
| assert(!empty()); |
| return m_pq.top(); |
| } |
| |
| // Erases the largest int in the container. |
| void |
| pop(); |
| |
| // Erases an arbitrary int. If the int is not in the container, this |
| // is a no-op, and the return value is false. |
| bool |
| erase(const int& r_str); |
| |
| bool |
| empty() const |
| { return m_pq.empty(); } |
| |
| size_t |
| size() const |
| { return m_pq.size(); } |
| |
| private: |
| // A priority queue of strings. |
| typedef pb_ds::priority_queue< int> pq_t; |
| |
| // A hash-table mapping strings to point_iterators inside the |
| // priority queue. |
| typedef cc_hash_table< int, pq_t::point_iterator> map_t; |
| |
| pq_t m_pq; |
| map_t m_map; |
| }; |
| |
| void |
| mapped_priority_queue:: |
| push(const int& r_str) |
| { |
| // First check if the int is already in the container. If so, just return. |
| if (m_map.find(r_str) != m_map.end()) |
| return; |
| |
| // Push the int into the priority queue, and store a point_iterator to it. |
| pq_t::point_iterator pq_it = m_pq.push(r_str); |
| |
| try |
| { |
| // Now make the map associate the int to the point_iterator. |
| m_map[r_str] = pq_it; |
| } |
| catch(...) |
| { |
| // If the above failed, we need to remove the int from the |
| // priority queue as well. |
| m_pq.erase(pq_it); |
| throw; |
| } |
| } |
| |
| void |
| mapped_priority_queue:: |
| pop() |
| { |
| assert(!empty()); |
| |
| // Erase the int from the map. |
| m_map.erase(m_pq.top()); |
| |
| // ...then from the priority queue. |
| m_pq.pop(); |
| } |
| |
| bool |
| mapped_priority_queue:: |
| erase(const int& r_str) |
| { |
| map_t::point_iterator map_it = m_map.find(r_str); |
| |
| // If the int is not in the map, this is a no-op. |
| if (map_it == m_map.end()) |
| return false; |
| |
| // Otherwise, we erase it from the priority queue. |
| m_pq.erase(map_it->second); |
| |
| // ...then from the map. |
| m_map.erase(r_str); |
| |
| return true; |
| } |
| |
| int main() |
| { |
| // Push some values into the container object. |
| mapped_priority_queue m; |
| m.push(1); |
| m.push(2); |
| |
| // The following four operations are no-ops: 2 and 1 are already in |
| // the container. |
| m.push(2); |
| m.push(2); |
| m.push(2); |
| m.push(1); |
| |
| m.push(10); |
| m.push(11); |
| m.push(12); |
| |
| // The size should be 5, since m contains the set {1, 2, 10, 11, 12}. |
| assert(m.size() == 5); |
| |
| // The largest value should be 12. |
| assert(m.top() == 12); |
| |
| // Now erase some values. |
| |
| // Erasing 1 actually erases a value. |
| assert(m.erase(1)); |
| |
| // ...but erasing 1 again is a no-op. |
| assert(!m.erase(1)); |
| |
| // The size should be 5, since m contains the set {2, 10, 11, 12}. |
| assert(m.size() == 4); |
| |
| // Now print the values in the container. |
| while (!m.empty()) |
| { |
| cout << m.top() << endl; |
| m.pop(); |
| } |
| |
| return 0; |
| } |
| |