110 lines
3.2 KiB
C++
110 lines
3.2 KiB
C++
/*
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* Copyright (C) 2011 Apple Inc. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
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* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
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* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
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* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#pragma once
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#include <wtf/Assertions.h>
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namespace WTF {
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// A UnionFind class can be used to compute disjoint sets using the
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// disjoint-set forest data structure. Each UnionFind instance is a
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// node in the forest. Typically you use it by using UnionFind as a
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// superclass:
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//
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// class MemberOfSet : public UnionFind<MemberOfSet> { ... }
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//
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// Calling x->find() gives you a MemberOfSet* that represents the
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// disjoint set that x belongs to. Calling x->unify(y) unifies x's
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// set with y's set, and ensures that:
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//
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// x->find() == y->find()
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//
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// and that:
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//
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// a->find() == b->find()
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//
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// for any a, b if prior to the call to x->unify(y), we would have
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// had:
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//
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// a->find() == x
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// b->find() == y
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//
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// This implementation is almost amortized O(1), but could be worse
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// in unlikely pathological cases. It favors having a non-recursive
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// single pass implementation of unify() and find() over ensuring the
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// theoretical O(InverseAckermann[n]) amortized bound, which is much
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// closer to amortized O(1).
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template<typename T>
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class UnionFind {
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public:
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UnionFind()
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: m_parent(0)
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{
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}
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bool isRoot() const
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{
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bool result = !m_parent;
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ASSERT(result == (const_cast<UnionFind<T>*>(this)->find() == this));
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return result;
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}
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T* find()
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{
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T* result = static_cast<T*>(this);
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T* next = result->m_parent;
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while (next) {
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result = next;
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next = result->m_parent;
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}
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ASSERT(result);
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if (result != this)
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m_parent = result;
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return result;
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}
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void unify(T* other)
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{
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T* a = static_cast<T*>(this)->find();
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T* b = other->find();
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ASSERT(!a->m_parent);
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ASSERT(!b->m_parent);
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if (a == b)
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return;
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a->m_parent = b;
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}
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private:
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T* m_parent;
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};
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} // namespace WTF
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using WTF::UnionFind;
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