adding a method to get the successor of a node inside the birany sear…

…ch tree data structure

src/data-structures/tree/binary-search-tree/BinarySearchTreeNode.js

@@ -148,4 +148,23 @@ export default class BinarySearchTreeNode extends BinaryTreeNode {
 
     return this.left.findMin();
   }
+
+  /**
+   * @return {BinarySearchTreeNode}
+   */
+  successor() {
+    if (this.right) {
+      return this.right.findMin();
+    }
+
+    let currentNode = this;
+    let { parent } = currentNode;
+
+    while (parent !== null && parent.right && parent.right.value === currentNode.value) {
+      currentNode = parent;
+      parent = currentNode.parent;
+    }
+
+    return parent;
+  }
 }

src/data-structures/tree/binary-search-tree/__test__/BinarySearchTreeNode.test.js

@@ -252,4 +252,21 @@ describe('BinarySearchTreeNode', () => {
 
     expect(childNode.parent).toBeNull();
   });
+
+  it('should get the successor of a node', () => {
+    const rootNode = new BinarySearchTreeNode(5);
+    rootNode.insert(2);
+    rootNode.insert(3);
+    rootNode.insert(1);
+    rootNode.insert(7);
+    rootNode.insert(6);
+
+    const node = rootNode.find(1);
+    const node2 = rootNode.find(6);
+    const node3 = rootNode.find(7);
+
+    expect(node.successor().value).toBe(2);
+    expect(node2.successor().value).toBe(7);
+    expect(node3.successor()).toBeNull();
+  });
 });