Merge pull request amejiarosario#34 from amejiarosario/beblueblue-question

fix(avl-tree): balance was not working properly

Author: amejiarosario

CHANGELOG.md

@@ -13,6 +13,15 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Bug Fixes (patch)
 
+## [1.3.7]
+
+### Breaking Changes (major)
+
+### New Features (minor)
+
+### Bug Fixes (patch)
+- fix(avl-tree): balance was not working properly [commit](https://github.com/amejiarosario/dsa.js/commit/98e2c037f05caf37731da1dc50dd8867a1804c0e)
+
 ## [1.3.6]
 
 ### Breaking Changes (major)
@@ -21,7 +30,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Bug Fixes (patch)
 - update deps [commit](https://github.com/amejiarosario/dsa.js/commit/d8ce2f5b1a3bfeb861928d6c99d7624cd9ac144a)
-- style: fix eslint issue [commit](https://github.com/amejiarosario/dsa.js/commit/72e3d68e09bb9c7dd3fabf5cbeba1ae5571fc686)%
+- style: fix eslint issue [commit](https://github.com/amejiarosario/dsa.js/commit/72e3d68e09bb9c7dd3fabf5cbeba1ae5571fc686)
 
 ## [1.3.5]
 
@@ -116,7 +125,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 -
 
-[Unreleased]: https://github.com/amejiarosario/dsa.js/compare/1.3.6...HEAD
+[Unreleased]: https://github.com/amejiarosario/dsa.js/compare/1.3.7...HEAD
+[1.3.6]: https://github.com/amejiarosario/dsa.js/compare/1.3.6...1.3.7
 [1.3.6]: https://github.com/amejiarosario/dsa.js/compare/1.3.5...1.3.6
 [1.3.5]: https://github.com/amejiarosario/dsa.js/compare/1.3.4...1.3.5
 [1.3.4]: https://github.com/amejiarosario/dsa.js/compare/1.2.3...1.3.4

notes.md

@@ -22,9 +22,9 @@ git log <last tag> HEAD --pretty=format:%s
 # example
 git log 1.1.0..HEAD --pretty=format:%s
 
-git log 1.3.4..HEAD --pretty=format:"- %s [commit](https://github.com/amejiarosario/dsa.js/commit/%H)" --grep "BREAKING CHANGE:"
-git log 1.3.4..HEAD --pretty=format:"- %s [commit](https://github.com/amejiarosario/dsa.js/commit/%H)" --grep "^feat.*:"
-git log 1.3.4..HEAD --pretty=format:"- %s [commit](https://github.com/amejiarosario/dsa.js/commit/%H)" --grep "^fix.*:"
+git log 1.3.6..HEAD --pretty=format:"- %s [commit](https://github.com/amejiarosario/dsa.js/commit/%H)" --grep "BREAKING CHANGE:"
+git log 1.3.6..HEAD --pretty=format:"- %s [commit](https://github.com/amejiarosario/dsa.js/commit/%H)" --grep "^feat.*:"
+git log 1.3.6..HEAD --pretty=format:"- %s [commit](https://github.com/amejiarosario/dsa.js/commit/%H)" --grep "^fix.*:"
 ```
 
 New features in this release

package.json

@@ -1,6 +1,6 @@
 {
   "name": "dsa.js",
-  "version": "1.3.6",
+  "version": "1.3.7",
   "description": "Data Structures & Algorithms in JS",
   "author": "Adrian Mejia <hi+dsajs@adrianmejia.com> (https://adrianmejia.com)",
   "homepage": "https://github.com/amejiarosario/dsa.js",

src/data-structures/trees/avl-tree.js

@@ -17,23 +17,21 @@ const {
  * - LR rotations: double rotation left-right
  * - RL rotations: double rotation right-left
  *
- * @param {TreeNode} node
+ * @param {BinaryTreeNode} node
  */
 function balance(node) {
   if (node.balanceFactor > 1) {
     // left subtree is higher than right subtree
-    if (node.left.balanceFactor > 0) {
-      return rightRotation(node);
-    } if (node.left.balanceFactor < 0) {
+    if (node.left.balanceFactor < 0) {
       return leftRightRotation(node);
     }
-  } else if (node.balanceFactor < -1) {
+    return rightRotation(node);
+  } if (node.balanceFactor < -1) {
     // right subtree is higher than left subtree
-    if (node.right.balanceFactor < 0) {
-      return leftRotation(node);
-    } if (node.right.balanceFactor > 0) {
+    if (node.right.balanceFactor > 0) {
       return rightLeftRotation(node);
     }
+    return leftRotation(node);
   }
   return node;
 }
@@ -43,7 +41,7 @@ function balance(node) {
 /**
  * Bubbles up balancing nodes a their parents
  *
- * @param {TreeNode} node
+ * @param {BinaryTreeNode} node
  */
 function balanceUpstream(node) {
   let current = node;

src/data-structures/trees/avl-tree.spec.js

@@ -165,4 +165,65 @@ describe('AvlTree', () => {
         null, null, null, null, null, null]);
     });
   });
+
+  describe('balancing to the left', () => {
+    let n32;
+    beforeEach(() => {
+      n32 = tree.add(32);
+      tree.add(8);
+      tree.add(64);
+      tree.add(4);
+      tree.add(16);
+      tree.add(48);
+      tree.add(128);
+      tree.add(2);
+      tree.add(6);
+      tree.add(10);
+      tree.add(20);
+    });
+
+    it('should have all nodes', () => {
+      expect(tree.toArray()).toEqual([32, 8, 64, 4, 16, 48, 128, 2, 6, 10, 20,
+        null, null, null, null, null, null, null, null, null, null, null, null]);
+    });
+
+    it('should rebalance when removing', () => {
+      tree.remove(64);
+      expect(tree.toArray()).toEqual([32, 8, 128, 4, 16, 48, null, 2, 6, 10, 20,
+        null, null, null, null, null, null, null, null, null, null]);
+      expect(n32.balanceFactor).toBe(1);
+      expect(n32.right.balanceFactor).toBe(1);
+      expect(n32.left.balanceFactor).toBe(0);
+
+      tree.remove(48);
+      expect(tree.toArray()).toEqual([8, 4, 32, 2, 6, 16, 128, null, null, null, null, 10, 20,
+        null, null, null, null, null, null]);
+    });
+  });
+
+  describe('balancing to the right', () => {
+    beforeEach(() => {
+      tree.add(8);
+      tree.add(4);
+      tree.add(32);
+      tree.add(2);
+      tree.add(16);
+      tree.add(64);
+      tree.add(10);
+      tree.add(20);
+      tree.add(60);
+      tree.add(70);
+    });
+
+    it('should build the tree', () => {
+      expect(tree.toArray()).toEqual([8, 4, 32, 2, null, 16, 64, null, null, 10, 20, 60, 70,
+        null, null, null, null, null, null, null, null]);
+    });
+
+    it('should rebalance right side', () => {
+      tree.remove(2);
+      expect(tree.toArray()).toEqual([32, 8, 64, 4, 16, 60, 70, null, null, 10, 20,
+        null, null, null, null, null, null, null, null]);
+    });
+  });
 });