Feature/add find non exact key

Readme.md

@@ -53,6 +53,8 @@ Or use the compiled version 'dist/splay.js'.
 - `tree.remove(key:any)` - Remove item
 - `tree.find(key):Node|Null` - Return node by its key
 - `tree.findStatic(key):Node|Null` - Return node by its key (doesn't re-balance the tree)
+- `tree.findAtOrNeighbor(key):Node|Null` - Return node by its key or a node with a key right above or below. Useful for floating point keys, etc.
+- `tree.findAtOrNeighborStatic(key):Node|Null` - Same as above, but doesn't re-balance the tree
 - `tree.at(index:Number):Node|Null` - Return node by its index in sorted order of keys
 - `tree.contains(key):Boolean` - Whether a node with the given key is in the tree
 - `tree.forEach(function(node) {...}):Tree` In-order traversal

src/index.ts

@@ -260,31 +260,49 @@ export default class Tree<Key=number, Value=any> {
     return null;
   }
 
+  public findAtOrNeighborStatic (key:Key) : Node<Key, Value>|null {
+    let current = this._root;
+    const compare = this._comparator;
+    let next:Node<Key, Value>;
+    while (current) {
+      const cmp = compare(key, current.key);
+      if (cmp === 0)  return current;
+      else if (cmp < 0) next = current.left;
+      else next = current.right;
+
+      if (next == undefined) return current;
+
+      current = next;
+    }
+  }
+
 
   /**
    * Find without splaying
    */
   public findStatic (key:Key) : Node<Key, Value>|null {
-    let current   = this._root;
-    const compare = this._comparator;
-    while (current) {
-      const cmp = compare(key, current.key);
-      if (cmp === 0)    return current;
-      else if (cmp < 0) current = current.left;
-      else              current = current.right;
+    const result_candidate = this.findAtOrNeighborStatic(key);
+    if (result_candidate && this._comparator(result_candidate.key, key) === 0) {
+      return result_candidate;
     }
     return null;
   }
 
-
-  public find (key:Key) : Node<Key, Value>|null {
+  public findAtOrNeighbor (key:Key) : Node<Key, Value>|null {
     if (this._root) {
       this._root = splay(key, this._root, this._comparator);
-      if (this._comparator(key, this._root.key) !== 0) return null;
     }
     return this._root;
   }
 
+  public find (key:Key) : Node<Key, Value>|null {
+    const result_candidate = this.findAtOrNeighbor(key);
+    if (result_candidate && this._comparator(result_candidate.key, key) === 0) {
+      return result_candidate;
+    }
+    return null;
+  }
+
 
   public contains (key:Key) : boolean {
     let current   = this._root;

tests/find.test.ts

@@ -56,4 +56,66 @@ describe ('find', () => {
 
     assert.strictEqual(tree.find(2), tree.root);
   });
+
+  it('should return previous key as result of search', () => {
+    const tree = new Tree<Number,any>();
+    assert.equal(tree.findAtOrNeighbor(10), null);
+    assert.equal(tree.findAtOrNeighbor(20), null);
+    assert.equal(tree.findAtOrNeighbor(30), null);
+    tree.insert(10, 40);
+    tree.insert(20, 50);
+    tree.insert(30, 60);
+
+    let root = tree.root;
+    assert.equal(tree.findAtOrNeighbor(10).data, 40);
+    assert.notStrictEqual(root, tree.root);
+    root = tree.root;
+
+    const found_around_15 = tree.findAtOrNeighbor(15);
+    assert.equal(found_around_15.data === 40 || found_around_15.data === 50, true);
+
+    assert.equal(tree.findAtOrNeighbor(20).data, 50);
+    assert.notStrictEqual(root, tree.root);
+    root = tree.root;
+
+    assert.equal(tree.findAtOrNeighbor(30).data, 60);
+    assert.notStrictEqual(root, tree.root);
+    root = tree.root;
+
+    assert.equal(tree.findAtOrNeighbor(80).data, 60);
+    assert.strictEqual(root, tree.root);
+  });
+
+  it ('should allow finding node by approximate key without splaying', () => {
+    const tree = new Tree<Number,any>();
+    assert.equal(tree.findAtOrNeighborStatic(10), null);
+    assert.equal(tree.findAtOrNeighborStatic(20), null);
+    assert.equal(tree.findAtOrNeighborStatic(30), null);
+    tree.insert(-20, 80);
+    tree.insert(10, 40);
+    tree.insert(20, 50);
+    tree.insert(30, 60);
+
+    tree.find(20);
+    const root = tree.root;
+    assert.equal(tree.findAtOrNeighborStatic(10).data, 40);
+    assert.strictEqual(root, tree.root);
+
+    const result_around_15 = tree.findAtOrNeighborStatic(15);
+    assert.equal(result_around_15.data === 40 || result_around_15.data === 50, true);
+    assert.strictEqual(root, tree.root);
+
+    assert.equal(tree.findAtOrNeighborStatic(20).data, 50);
+    assert.strictEqual(root, tree.root);
+
+    assert.equal(tree.findAtOrNeighborStatic(30).data, 60);
+    assert.strictEqual(root, tree.root);
+
+    assert.equal(tree.findAtOrNeighborStatic(80).data, 60);
+
+    assert.equal(tree.findAtOrNeighborStatic(-20).data, 80);
+    assert.equal(tree.findAtOrNeighborStatic(-30).data, 80);
+
+    assert.strictEqual(tree.find(20), tree.root);
+  });
 });