fix 2 functions of RedBlackTree, write tests

src/data-structures/tree/red-black-tree/RedBlackTree.js

@@ -184,8 +184,13 @@ export default class RedBlackTree extends BinarySearchTree {
     parentNode.setRight(childLeftNode);
 
     // Put left-right node in place of left node.
+    // It sets previous grandParentNode.left.parent = null
+    // (previous grandParentNode.left is parentNode).
     grandParentNode.setLeft(childNode);
 
+    // Set correct parent of parentNode.
+    parentNode.parent = childNode;
+
     // Now we're ready to do left-left rotation.
     return this.leftLeftRotation(grandParentNode);
   }
@@ -259,8 +264,13 @@ export default class RedBlackTree extends BinarySearchTree {
     parentNode.setLeft(childRightNode);
 
     // Put childNode node in place of parentNode.
+    // It sets previous grandParentNode.right.parent = null
+    // (previous grandParentNode.right is parentNode).
     grandParentNode.setRight(childNode);
 
+    // Set correct parent of parentNode.
+    parentNode.parent = childNode;
+
     // Now we're ready to do right-right rotation.
     return this.rightRightRotation(grandParentNode);
   }

src/data-structures/tree/red-black-tree/__test__/RedBlackTree.test.js

@@ -321,4 +321,47 @@ describe('RedBlackTree', () => {
 
     expect(removeNodeFromRedBlackTree).toThrowError();
   });
+
+  it('should set parent of parent node correctly in first part of leftRightRotation', () => {
+    const tree = new RedBlackTree();
+
+    tree.insert(15);
+    tree.insert(100);
+    tree.insert(7);
+    const node1 = tree.insert(1);
+    // now 15 is root, 7 is his left child, 100 is right, 1 is left child of 7
+    const node5 = tree.insert(5);
+    // rotation: at first, 7 is Grandparent, 1 is his left child and Parent of his right Child 5
+    // . 7
+    // 1
+    // . 5
+    // after rotation 5 is parent of 1 and 7, 1 is left child, 7 is right child
+    // . 5
+    // 1 . 7
+    // so, 5.left = 1 and 1.parent = 5 (should be)
+    expect(node5.left).toBe(node1);
+    expect(node1.parent).toBe(node5);
+  });
+
+  it('should set parent of parent node correctly in first part of rightLeftRotation', () => {
+    const tree = new RedBlackTree();
+
+    tree.insert(15);
+    tree.insert(100);
+    tree.insert(7);
+    const node120 = tree.insert(120);
+    // now 15 is root, 7 is his left child, 100 is right, 120 is right child of 100
+    const node110 = tree.insert(110);
+    // rotation: at first, 100 is Grandparent,
+    // 120 is his right child and Parent of his left Child 110
+    // 100
+    // . 120
+    // 110
+    // after rotation 110 is parent of 100 and 120, 100 is left child, 120 is right child
+    // .. 110
+    // 100 . 120
+    // so, 110.right = 120 and 120.parent = 110 (should be)
+    expect(node110.right).toBe(node120);
+    expect(node120.parent).toBe(node110);
+  });
 });