1 // Copyright 2003 Adam Megacz, see the COPYING file for licensing [GPL]
4 // FEATURE: private void intersection() { }
5 // FEATURE: private void union() { }
6 // FEATURE: private void subset() { }
7 // FEATURE: grow if we run out of slots
10 /** a weight-balanced tree with fake leaves */
11 public class BalancedTree {
14 // Instance Variables ///////////////////////////////////////////////////////////////////
16 private int root = 0; ///< the slot of the root element
18 private int cached_index = 0;
19 private int cached_slot = 0;
21 // Public API //////////////////////////////////////////////////////////////////////////
23 /** the number of elements in the tree */
24 public final int treeSize() { return root == 0 ? 0 : size[root]; }
26 /** clamps index to [0..treeSize()] and inserts object o *before* the specified index */
27 public final void insertNode(int index, Object o) {
28 cached_slot = cached_index = 0;
29 if (index < 0) index = 0;
30 if (index > treeSize()) index = treeSize();
31 int arg = allocateSlot(o);
32 if (root != 0) { insert(index, arg, root, 0, false, false); return; }
39 /** clamps index to [0..treeSize()-1] and replaces the object at that index with object o */
40 public final void replaceNode(int index, Object o) {
41 cached_slot = cached_index = 0;
42 if (index < 0) index = 0;
43 if (index > treeSize()) index = treeSize() - 1;
44 int arg = allocateSlot(o);
45 if (root != 0) { insert(index, arg, root, 0, true, false); return; }
51 /** returns the index of o; runs in O((log n)^2) time unless cache hit */
52 public final int indexNode(Object o) {
53 if (objects[cached_slot] == o) return cached_index;
55 int slot = getSlot(o, o.hashCode() ^ this.hashCode());
56 int parent = -1 * left[leftmost(slot)];
57 if (parent == 0) return size(left[slot]); // we are on the far left edge
59 // all nodes after parent and before us are in our left subtree
60 else return size(left[slot]) + indexNode(objects[parent]) + 1;
63 /** returns the object at index; runs in O(log n) time unless cache hit */
64 public final Object getNode(int index) {
65 if (index == cached_index) return objects[cached_slot];
67 int distance = Math.abs(index - cached_index);
69 // if the in-order distance between the cached node and the
70 // target node is less than log(n), it's probably faster to
72 if (cached_index != 0 && (distance < 16) && ((2 << distance) < treeSize())) {
73 while(cached_index > index) { cached_slot = prev(cached_slot); cached_index--; }
74 while(cached_index < index) { cached_slot = next(cached_slot); cached_index++; }
75 return objects[cached_slot];
78 return objects[get(index, root)];
81 /** deletes the object at index, returning the deleted object */
82 public final Object deleteNode(int index) {
83 cached_slot = cached_index = 0;
84 return delete(index, root, 0);
88 // Node Data /////////////////////////////////////////////////////////////////////////
90 private final static int NUM_SLOTS = 265 * 1024;
93 * Every object inserted into *any* tree gets a "slot" in this
94 * array. The slot is determined by hashcode modulo the length of
95 * the array, with quadradic probing to resolve collisions. NOTE
96 * that the "slot" of a node is NOT the same as its index.
97 * Furthermore, if an object is inserted into multiple trees, that
98 * object will have multiple slots.
100 private static Object[] objects = new Object[NUM_SLOTS];
101 private static int[] left = new int[NUM_SLOTS]; ///< if positive: left child's slot; if negative: predecessor's slot
102 private static int[] right = new int[NUM_SLOTS]; ///< if positive: right child's slot; if negative: successor's slot
103 private static int[] size = new int[NUM_SLOTS]; ///< the number of descendants of this node *including the node itself*
106 // Slot Management //////////////////////////////////////////////////////////////////////
108 /** returns the slot holding object o; use null to allocate a new slot */
109 private int getSlot(Object o, int hash) {
110 // FIXME: check for full table
111 int dest = Math.abs(hash) % objects.length;
115 while (objects[dest] != o) {
116 if (dest == 0) dest++;
117 dest = Math.abs((odest + (plus ? 1 : -1) * tries * tries) % objects.length);
124 /** allocates a new slot */
125 private int allocateSlot(Object o) {
126 // we XOR with our own hashcode so that we don't get tons of
127 // collisions when a single Object is inserted into multiple
129 int slot = getSlot(null, o.hashCode() ^ this.hashCode());
136 // Helpers /////////////////////////////////////////////////////////////////////////
138 private final int leftmost(int slot) { return left[slot] <= 0 ? slot : leftmost(left[slot]); }
139 private final int rightmost(int slot) { return right[slot] <= 0 ? slot : rightmost(right[slot]); }
140 private final int next(int slot) { return right[slot] <= 0 ? -1 * right[slot] : leftmost(right[slot]); }
141 private final int prev(int slot) { return left[slot] <= 0 ? -1 * left[slot] : rightmost(left[slot]); }
142 private final int size(int slot) { return slot <= 0 ? 0 : size[slot]; }
145 // Rotation and Balancing /////////////////////////////////////////////////////////////
154 // FIXME might be doing too much work here
155 private void rotate(boolean toTheLeft, int b, int parent) {
156 int[] left = toTheLeft ? BalancedTree.left : BalancedTree.right;
157 int[] right = toTheLeft ? BalancedTree.right : BalancedTree.left;
162 if (parent == 0) root = d;
163 else if (left[parent] == b) left[parent] = d;
164 else if (right[parent] == b) right[parent] = d;
165 else throw new Error("rotate called with invalid parent");
166 size[b] = 1 + size(left[b]) + size(right[b]);
168 size[d] = 1 + size(left[d]) + size(right[d]);
172 private void balance(int slot, int parent) {
173 if (size(left[slot]) - 1 > 2 * size(right[slot])) rotate(false, slot, parent);
174 else if (size(left[slot]) * 2 < size(right[slot]) - 1) rotate(true, slot, parent);
175 size[slot] = 1 + size(left[slot]) + size(right[slot]);
180 // Insert /////////////////////////////////////////////////////////////////////////
182 private void insert(int index, int arg, int slot, int parent, boolean replace, boolean wentLeft) {
183 int diff = slot <= 0 ? 0 : index - size(left[slot]);
184 if (slot > 0 && diff != 0) {
185 if (diff < 0) insert(index, arg, left[slot], slot, replace, true);
186 else insert(index - size(left[slot]) - 1, arg, right[slot], slot, replace, false);
187 balance(slot, parent);
191 if (size[arg] != 0) throw new Error("double insertion");
193 // we become the child of a former leaf
195 int[] left = wentLeft ? BalancedTree.left : BalancedTree.right;
196 int[] right = wentLeft ? BalancedTree.right : BalancedTree.left;
199 right[arg] = -1 * parent;
200 balance(arg, parent);
202 // we take the place of a preexisting node
204 left[arg] = left[slot]; // steal slot's left subtree
205 left[slot] = -1 * arg;
206 right[arg] = slot; // make slot our right subtree
211 (left[parent] == slot ? left : right)[parent] = arg;
213 balance(arg, parent);
219 // Retrieval //////////////////////////////////////////////////////////////////////
221 private int get(int index, int slot) {
222 int diff = index - size(left[slot]);
223 if (diff > 0) return get(diff - 1, right[slot]);
224 else if (diff < 0) return get(index, left[slot]);
229 // Deletion //////////////////////////////////////////////////////////////////////
231 private Object delete(int index, int slot, int parent) {
232 int diff = index - size(left[slot]);
234 Object ret = delete(index, left[slot], slot);
235 balance(slot, parent);
238 } else if (diff > 0) {
239 Object ret = delete(diff - 1, right[slot], slot);
240 balance(slot, parent);
244 if (left[slot] == 0) {
245 if (parent == 0) root = right[slot];
246 else (left[parent] == slot ? left : right)[parent] = right[slot];
248 balance(slot, parent);
249 } else if (right[slot] == 0) {
250 if (parent == 0) root = left[slot];
251 else (left[parent] == slot ? left : right)[parent] = left[slot];
253 balance(slot, parent);
255 Object replacement_object = delete(index - 1, slot, parent);
256 int replacement = allocateSlot(replacement_object);
257 if (replacement != 0) {
258 left[replacement] = left[slot];
259 right[replacement] = right[slot];
261 if (parent == 0) root = replacement;
262 else (left[parent] == slot ? left : right)[parent] = replacement;
265 balance(replacement, parent);
267 Object ret = objects[slot];
269 objects[slot] = null;