252 lines
8.5 KiB
C++
252 lines
8.5 KiB
C++
// Copyright (c) 1997-2000
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// Utrecht University (The Netherlands),
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// ETH Zurich (Switzerland),
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// INRIA Sophia-Antipolis (France),
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// Max-Planck-Institute Saarbruecken (Germany),
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// and Tel-Aviv University (Israel). All rights reserved.
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//
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// This file is part of CGAL (www.cgal.org)
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//
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// $URL: https://github.com/CGAL/cgal/blob/v5.1/Union_find/include/CGAL/Union_find.h $
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// $Id: Union_find.h fcd4e57 2020-05-22T11:29:03+02:00 Marc Glisse
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// SPDX-License-Identifier: LGPL-3.0-or-later OR LicenseRef-Commercial
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//
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//
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// Author(s) : Michael Seel <seel@mpi-sb.mpg.de>,
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// Lutz Kettner <kettner@mpi-sb.mpg.de>
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#ifndef CGAL_UNION_FIND_H
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#define CGAL_UNION_FIND_H
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#include <CGAL/basic.h>
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#include <CGAL/memory.h>
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#include <cstddef>
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namespace CGAL {
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namespace internal {
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template <class PTR_, class V_, class R_, class P_>
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class UF_forward_iterator {
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PTR_ m_p;
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public:
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// should be private and Union_find<...> a friend.
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PTR_ ptr() const { return m_p; }
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typedef UF_forward_iterator<PTR_, V_, R_, P_> Self;
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typedef V_ value_type;
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typedef R_ reference;
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typedef P_ pointer;
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typedef std::forward_iterator_tag iterator_category;
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UF_forward_iterator() : m_p(0) {}
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UF_forward_iterator(PTR_ p) : m_p(p) {}
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// Allows construction of const_iterator from iterator
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template <class PPTR, class VV, class RR, class PP>
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UF_forward_iterator(const UF_forward_iterator<PPTR, VV, RR, PP>& i)
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: m_p(i.ptr()) {}
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bool operator==( const Self& x) const { return m_p == x.m_p; }
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bool operator!=( const Self& x) const { return !(*this == x); }
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bool operator<(const Self& other) const{ return m_p<other.m_p; }
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bool operator>(const Self& other) const{ return m_p>other.m_p; }
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bool operator<=(const Self& other) const{ return m_p<=other.m_p; }
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bool operator>=(const Self& other) const{ return m_p>=other.m_p; }
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reference operator*() const { return m_p->value; }
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pointer operator->() const { return &(m_p->value); }
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Self& operator++() {
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CGAL_assertion(m_p != 0);
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m_p = m_p->next;
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return *this;
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}
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Self operator++(int) {
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Self tmp = *this;
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++*this;
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return tmp;
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}
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};
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} // internal
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// Union-Find with path compression.
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// --------------------------------------------------------------------
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// An instance of the data type Union_find is a partition of values of
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// type |T| into disjoint sets. The type |A| has to be a model of the
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// allocator concept as defined in the C++ standard.
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// Union_find is implemented with union by rank and path compression.
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// The running time for $m$ set operations on $n$ elements is
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// $O(n \alpha(m,n))$ where $\alpha(m,n)$ is the extremely slow
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// growing inverse of Ackermann's function.
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template <typename T, typename A = CGAL_ALLOCATOR(T) >
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class Union_find {
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struct Union_find_struct {
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typedef Union_find_struct* pointer;
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// friend class Union_find<T,A>;
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mutable pointer up;
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pointer next;
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std::size_t size;
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T value;
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Union_find_struct( pointer n, const T& x)
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: up(0), next(n), size(1), value(x) {}
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};
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public:
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typedef Union_find<T,A> Self;
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typedef Union_find_struct* pointer;
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typedef const Union_find_struct* const_pointer;
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typedef T value_type;
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typedef T& reference;
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typedef const T& const_reference;
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typedef internal::UF_forward_iterator< pointer, T, T&, T*> iterator;
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typedef iterator handle;
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typedef internal::UF_forward_iterator< const_pointer, T, const T&, const T*>
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const_iterator;
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typedef const_iterator const_handle;
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#ifdef _MSC_VER
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typedef CGAL_ALLOCATOR(Union_find_struct) allocator;
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#else
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typedef typename std::allocator_traits<A>::template rebind_alloc<Union_find_struct> allocator;
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#endif
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private:
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pointer m_first;
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std::size_t sets;
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std::size_t values;
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allocator alloc;
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// Private decl. and no definition, thus no copy constructor
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// and no assignment for this class.
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Union_find(const Self&);
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Self& operator=(const Self&);
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pointer find( pointer p) const {
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CGAL_assertion(p != 0);
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pointer r = p;
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while (r->up)
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r = r->up; // now r is the root;
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while (p->up) {
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pointer u = p->up;
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p->up = r; // path compression: assign root r as new parent
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p = u; // this would need the 'mutable' for the up field
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} // if we would have a const_pointer, see the cast
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return r; // in the fct. below. We keep the mutable as reminder.
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}
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const_pointer find( const_pointer p ) const {
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return find( const_cast<pointer>(p));
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}
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bool is_valid(const_handle v) const { return v != const_handle(0); }
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public:
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Union_find() : m_first(0), sets(0), values(0) {}
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~Union_find() { clear(); }
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allocator get_allocator() const { return alloc; }
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std::size_t number_of_sets() const { return sets; }
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// returns the number of disjoint sets
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std::size_t size() const { return values; }
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// returns the number of values
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std::size_t bytes() const {
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// returns the memory consumed
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return values * sizeof(Union_find_struct) + sizeof( Self);
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}
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std::size_t size( const_handle p) const { return find(p).ptr()->size; }
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// returns the size of the set containing $p$
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void clear();
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// reinitializes to an empty partition
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handle make_set(const T& x);
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// creates a new singleton set containing |x| and returns a handle to it
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handle push_back(const T& x) { return make_set(x); }
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// same as |make_set(x)|
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template <class Forward_iterator>
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void insert( Forward_iterator first, Forward_iterator beyond) {
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// insert the range of values referenced by |[first,beyond)|.
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// Precond: value type of |Forward_iterator| is |T|.
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while (first != beyond)
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push_back(*first++);
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}
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handle find( handle p) const { return find(p.ptr()); }
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const_handle find( const_handle p ) const {
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// returns a canonical handle of the set that contains |p|,
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// i.e., |P.same_set(p,q)| iff |P.find(p)| and |P.find(q)| return
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// the same handle. Precond: |p| is a handle in the union find structure.
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return find(p.ptr());
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}
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void unify_sets(handle p, handle q);
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// unites the sets of partition containing $p$ and $q$.
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// Precond: $p$ and $q$ are in the partition.
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bool same_set( const_handle p, const_handle q) const {
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// returns true iff $p$ and $q$ belong to the same set.
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// Precond: $p$ and $q$ are in the partition.
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return find(p) == find(q);
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}
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iterator begin() { return iterator(m_first); }
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iterator end() { return iterator(0); }
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const_iterator begin() const { return const_iterator(m_first); }
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const_iterator end() const { return const_iterator(0); }
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};
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template <typename T, typename A>
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typename Union_find<T,A>::handle Union_find<T,A>::make_set(const T& x) {
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pointer tmp = m_first;
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m_first = alloc.allocate(1);
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std::allocator_traits<allocator>::construct(alloc, m_first, tmp, x);
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++sets;
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++values;
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return handle( m_first);
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}
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template <typename T, typename A>
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void Union_find<T,A>::clear() {
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while (m_first) {
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pointer tmp = m_first->next;
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std::allocator_traits<allocator>::destroy(alloc, m_first);
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alloc.deallocate(m_first,1);
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m_first = tmp;
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}
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sets = 0;
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values = 0;
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}
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template <typename T, typename A>
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void Union_find<T,A>::unify_sets( handle p, handle q) {
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CGAL_assertion( is_valid(p) && is_valid(q));
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pointer pit = find( p.ptr());
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pointer qit = find( q.ptr());
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if (pit == qit)
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return;
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std::size_t sp = pit->size;
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std::size_t sq = qit->size;
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if (sp > sq)
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std::swap(pit,qit); // now sp <= sq
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pit->up = qit; // linking roots
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qit->size += pit->size; // updating size
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--sets;
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}
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} //namespace CGAL
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#endif // CGAL_UNION_FIND_H
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