add left-leaning red-black tree (llrb.js)

Author: mourner

llrb.js

@@ -0,0 +1,85 @@
+
+module.exports = llrb;
+
+function llrb(compare) {
+    return new LLRBTree(compare);
+}
+
+function LLRBTree(compare) {
+    this.compare = compare || defaultCompare;
+}
+
+function Node(key, value, red) {
+    this.key = key;
+    this.value = value;
+    this.red = red;
+    this.left = null;
+    this.right = null;
+}
+
+LLRBTree.prototype = {
+    find: function (key) {
+        var x = this.root,
+            compare = this.compare;
+        while (x) {
+            var c = compare(key, x.key);
+            if (c === 0) return x;
+            x = c < 0 ? x.left : x.right;
+        }
+        return null;
+    },
+
+    insert: function (key, value) {
+        this.root = insert(this.root, key, value, this.compare);
+        this.root.red = false;
+    }
+}
+
+function defaultCompare(a, b) {
+    return a < b ? -1 :
+           a > b ?  1 : 0;
+}
+
+function insert(h, key, value, compare) {
+    if (!h) return new Node(key, value, true);
+
+    var c = compare(key, h.key);
+
+    if (c < 0) h.left = insert(h.left, key, value, compare);
+    else if (c > 0) h.right = insert(h.right, key, value, compare);
+    else h.value = value;
+
+    if (isRed(h.right) && !isRed(h.left)) h = rotateLeft(h);
+    if (isRed(h.left) && isRed(h.left.left)) h = rotateRight(h);
+    if (isRed(h.left) && isRed(h.right)) flipColors(h);
+
+    return h;
+}
+
+function isRed(h) {
+    return h && h.red;
+}
+
+function rotateRight(h) {
+    var x = h.left;
+    h.left = x.right;
+    x.right = h;
+    x.red = h.red;
+    h.red = true;
+    return x;
+}
+
+function rotateLeft(h) {
+    var x = h.right;
+    h.right = x.left;
+    x.left = h;
+    x.red = h.red;
+    h.red = true;
+    return x;
+}
+
+function flipColors(h) {
+    h.red = true;
+    h.left.red = false;
+    h.right.red = false;
+}