+// Copyright 2003 Adam Megacz, see the COPYING file for licensing [GPL]
+package org.xwt.util;
+
+// Implemented from http://ciips.ee.uwa.edu.au/~morris/Year2/PLDS210/red_black.html
+
+// 1. Every node is either red or black.
+// 2. Every leaf node is black; if a red node has no right or left child,
+// pretend that an imaginary (sentinel) black node is there.
+// 3. If a node is red, then both its children are black.
+// 4. Every simple path from a node to a descendant leaf contains the
+// same number of black nodes.
+
+
+// FIXME: ability to ask for n^th node; requires a descendant count
+
+/** a red-black tree of arbitrary objects */
+public class RedBlackTree {
+
+ private static final boolean RED = false;
+ private static final boolean BLACK = true;
+
+ private static final int DELETE = 0;
+ private static final int INSERT = 1;
+
+ // These arrays are indexed by "slot", a totally meaningless number
+ // assigned to each object object[slot] has index index[slot] and
+ // color color[slot]. Note that slot 0 is reserved as "null".
+
+ // FEATURE: use a bitmask?
+ private int[] left; ///< if positive: left child's slot; if negative: predecessor's slot
+ private int[] right; ///< if positive: right child's slot; if negative: successor's slot
+ private int[] size; ///< the number of descendants of this node *including the node itself*
+ private Object[] objects; ///< every object in the tree has an entry here; ordering is completely random
+
+ private int root = 0; ///< the slot of the root element
+
+ private int freeslot = 0;
+
+ private int leftmost(int slot) { return left[slot] <= 0 ? slot : leftmost(left[slot]); }
+ private int rightmost(int slot) { return right[slot] <= 0 ? slot : rightmost(right[slot]); }
+ private int next(int slot) { return right[slot] <= 0 ? -1 * right[slot] : leftmost(right[slot]); }
+ private int prev(int slot) { return left[slot] <= 0 ? -1 * left[slot] : rightmost(left[slot]); }
+
+ // parent parent
+ // | |
+ // b d
+ // / \ / \
+ // a d < == > b e
+ // / \ / \
+ // c e a c
+ void rotate(boolean toTheLeft, int b, int parent) {
+ if (b == 0) throw new Error("rotate called on the null slot");
+ int[] left = toTheLeft ? this.left : this.right;
+ int[] right = toTheLeft ? this.right : this.left;
+ int d = right[b];
+ if (d == 0) throw new Error("attempted to rotate a node with only one child in the wrong direction");
+ int c = left[d];
+ left[d] = b;
+ right[b] = c;
+ size[b] -= size[d];
+ int csize = c <= 0 ? 0 : size[c] + 1;
+ size[b] += csize;
+ size[d] -= csize;
+ size[d] += size[b];
+ if (parent == 0) root = d;
+ else if (left[parent] == b) left[parent] = d;
+ else if (right[parent] == b) right[parent] = d;
+ else throw new Error("rotate called with invalid parent");
+ }
+
+ public void balance(int slot, int parent) {
+ if (slot == 0) return;
+ if (size[left[slot]] > 2 * size[right[slot]]) {
+ rotate(false, slot, parent);
+ } else if (size[left[slot]] * 2 < size[right[slot]]) {
+ rotate(true, slot, parent);
+ }
+ size[slot] = 1 + size[left[slot]] + size[right[slot]];
+ }
+
+ // FIXME: maintain fakeptrs
+
+
+ // private void intersection() { }
+ // private void union() { }
+ // private void subset() { }
+
+ private void insert(int idx, int arg, int slot, int parent) {
+
+ int diff = idx - size[left[slot]];
+ if (slot == 0 || diff == 0) {
+ if (size[arg] != 0) throw new Error("double insertion");
+
+ left[arg] = left[slot]; // steal slot's left subtree
+ left[slot] = 0;
+ right[arg] = slot; // make slot our right subtree
+
+ // FIXME: if slot == 0 we can't use it to figure out which end of parent we belong on
+ if (parent == 0) root = arg;
+ else (left[parent] == slot ? left : right)[parent] = arg;
+
+ balance(slot, arg);
+ balance(arg, slot);
+ return;
+ }
+
+ if (diff < 0) insert(idx, arg, left[slot], slot);
+ else insert(idx - size[left[slot]] - 1, arg, right[slot], slot);
+ balance(slot, parent);
+ }
+
+ private int indexOf(int slot) {
+ int parent = -1 * left[leftmost(slot)];
+ if (parent == 0) return size[left[slot]]; // we are on the far left edge
+ else return size[left[slot]] + indexOf(parent) + 1; // all nodes after parent and before us are in our left subtree
+ }
+
+ private int get(int idx, int slot) {
+ int diff = idx - size[left[slot]];
+ if (diff > 0) return get(diff - 1, right[slot]);
+ else if (diff < 0) return get(idx, left[slot]);
+ else return slot;
+ }
+
+ // return slot that was deleted
+ private int delete(int idx, int slot, int parent) {
+ int diff = idx - size[left[slot]];
+ if (slot == 0) return 0;
+ else if (diff < 0) {
+ int ret = delete(idx, left[slot], slot);
+ balance(slot, parent);
+ return ret;
+
+ } else if (diff > 0) {
+ int ret = delete(diff - 1, right[slot], slot);
+ balance(slot, parent);
+ return ret;
+
+ } else {
+ size[slot] = 0;
+ if (left[slot] == 0) {
+ if (parent == 0) root = right[slot];
+ else (left[parent] == slot ? left : right)[parent] = right[slot];
+ right[slot] = 0;
+ balance(slot, parent);
+ } else if (right[slot] == 0) {
+ if (parent == 0) root = left[slot];
+ else (left[parent] == slot ? left : right)[parent] = left[slot];
+ left[slot] = 0;
+ balance(slot, parent);
+ } else {
+ int replacement = delete(idx - 1, slot, parent);
+ if (replacement != 0) {
+ left[replacement] = left[slot];
+ right[replacement] = right[slot];
+ }
+ if (parent == 0) root = replacement;
+ else (left[parent] == slot ? left : right)[parent] = replacement;
+ left[slot] = 0;
+ right[slot] = 0;
+ balance(replacement, parent);
+ }
+ return slot;
+ }
+ }
+
+}
projects / org.ibex.core.git / commitdiff