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