Skip to content

HTTPS clone URL

Subversion checkout URL

You can clone with HTTPS or Subversion.

Download ZIP
tag: FENNEC_20_0b4_…
Fetching contributors…

Cannot retrieve contributors at this time

286 lines (250 sloc) 7.158 kb
/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
* vim: set ts=8 sw=4 et tw=99 ft=cpp:
*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
/**
* A sorted tree with optimal access times, where recently-accessed elements
* are faster to access again.
*/
#ifndef mozilla_SplayTree_h_
#define mozilla_SplayTree_h_
#include "mozilla/Assertions.h"
#include "mozilla/NullPtr.h"
namespace mozilla {
template<class T, class C>
class SplayTree;
template<typename T>
class SplayTreeNode
{
public:
template<class A, class B>
friend class SplayTree;
SplayTreeNode()
: left(nullptr), right(nullptr), parent(nullptr)
{}
private:
T* left;
T* right;
T* parent;
};
/**
* Class which represents a splay tree.
* Splay trees are balanced binary search trees for which search, insert and
* remove are all amortized O(log n), but where accessing a node makes it
* faster to access that node in the future.
*
* T indicates the type of tree elements, Comparator must have a static
* compare(const T&, const T&) method ordering the elements. The compare
* method must be free from side effects.
*/
template<typename T, class Comparator>
class SplayTree
{
T* root;
T* freeList;
public:
SplayTree()
: root(nullptr), freeList(nullptr)
{}
bool empty() const {
return !root;
}
bool contains(const T& v)
{
if (empty())
return false;
T* last = lookup(v);
splay(last);
checkCoherency(root, nullptr);
return Comparator::compare(v, *last) == 0;
}
bool insert(T* v)
{
MOZ_ASSERT(!contains(*v), "Duplicate elements are not allowed.");
if (!root) {
root = v;
return true;
}
T* last = lookup(*v);
int cmp = Comparator::compare(*v, *last);
T** parentPointer = (cmp < 0) ? &last->left : &last->right;
MOZ_ASSERT(!*parentPointer);
*parentPointer = v;
v->parent = last;
splay(v);
checkCoherency(root, nullptr);
return true;
}
T* remove(const T& v)
{
T* last = lookup(v);
MOZ_ASSERT(last, "This tree must contain the element being removed.");
MOZ_ASSERT(Comparator::compare(v, *last) == 0);
// Splay the tree so that the item to remove is the root.
splay(last);
MOZ_ASSERT(last == root);
// Find another node which can be swapped in for the root: either the
// rightmost child of the root's left, or the leftmost child of the
// root's right.
T* swap;
T* swapChild;
if (root->left) {
swap = root->left;
while (swap->right)
swap = swap->right;
swapChild = swap->left;
} else if (root->right) {
swap = root->right;
while (swap->left)
swap = swap->left;
swapChild = swap->right;
} else {
T* result = root;
root = nullptr;
return result;
}
// The selected node has at most one child, in swapChild. Detach it
// from the subtree by replacing it with that child.
if (swap == swap->parent->left)
swap->parent->left = swapChild;
else
swap->parent->right = swapChild;
if (swapChild)
swapChild->parent = swap->parent;
// Make the selected node the new root.
root = swap;
root->parent = nullptr;
root->left = last->left;
root->right = last->right;
if (root->left) {
root->left->parent = root;
}
if (root->right) {
root->right->parent = root;
}
checkCoherency(root, nullptr);
return last;
}
T* removeMin()
{
MOZ_ASSERT(root, "No min to remove!");
T* min = root;
while (min->left)
min = min->left;
return remove(*min);
}
private:
/**
* Returns the node in this comparing equal to |v|, or a node just greater or
* just less than |v| if there is no such node.
*/
T* lookup(const T& v)
{
MOZ_ASSERT(!empty());
T* node = root;
T* parent;
do {
parent = node;
int c = Comparator::compare(v, *node);
if (c == 0)
return node;
else if (c < 0)
node = node->left;
else
node = node->right;
} while (node);
return parent;
}
/**
* Rotate the tree until |node| is at the root of the tree. Performing
* the rotations in this fashion preserves the amortized balancing of
* the tree.
*/
void splay(T* node)
{
MOZ_ASSERT(node);
while (node != root) {
T* parent = node->parent;
if (parent == root) {
// Zig rotation.
rotate(node);
MOZ_ASSERT(node == root);
return;
}
T* grandparent = parent->parent;
if ((parent->left == node) == (grandparent->left == parent)) {
// Zig-zig rotation.
rotate(parent);
rotate(node);
} else {
// Zig-zag rotation.
rotate(node);
rotate(node);
}
}
}
void rotate(T* node)
{
// Rearrange nodes so that node becomes the parent of its current
// parent, while preserving the sortedness of the tree.
T* parent = node->parent;
if (parent->left == node) {
// x y
// y c ==> a x
// a b b c
parent->left = node->right;
if (node->right)
node->right->parent = parent;
node->right = parent;
} else {
MOZ_ASSERT(parent->right == node);
// x y
// a y ==> x c
// b c a b
parent->right = node->left;
if (node->left)
node->left->parent = parent;
node->left = parent;
}
node->parent = parent->parent;
parent->parent = node;
if (T* grandparent = node->parent) {
if (grandparent->left == parent)
grandparent->left = node;
else
grandparent->right = node;
} else {
root = node;
}
}
T* checkCoherency(T* node, T* minimum)
{
#ifdef DEBUG
MOZ_ASSERT_IF(root, !root->parent);
if (!node) {
MOZ_ASSERT(!root);
return nullptr;
}
MOZ_ASSERT_IF(!node->parent, node == root);
MOZ_ASSERT_IF(minimum, Comparator::compare(*minimum, *node) < 0);
if (node->left) {
MOZ_ASSERT(node->left->parent == node);
T* leftMaximum = checkCoherency(node->left, minimum);
MOZ_ASSERT(Comparator::compare(*leftMaximum, *node) < 0);
}
if (node->right) {
MOZ_ASSERT(node->right->parent == node);
return checkCoherency(node->right, node);
}
return node;
#else
return nullptr;
#endif
}
SplayTree(const SplayTree&) MOZ_DELETE;
void operator=(const SplayTree&) MOZ_DELETE;
};
} /* namespace mozilla */
#endif /* mozilla_SplayTree_h_ */
Jump to Line
Something went wrong with that request. Please try again.