Refactor BST.

Author: trekhleb

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

@@ -14,41 +14,7 @@ export default class BinarySearchTree {
   }
 
   remove(value) {
-    const nodeToRemove = this.root.find(value);
-
-    if (!nodeToRemove) {
-      throw new Error('Item not found in the tree');
-    }
-
-    const { parent } = nodeToRemove;
-
-    if (!nodeToRemove.left && !nodeToRemove.right) {
-      // Node is a leaf and thus has no children.
-      // Just remove the pointer to this node from the parent node.
-      parent.removeChild(nodeToRemove);
-    } else if (nodeToRemove.left && nodeToRemove.right) {
-      // Node has two children.
-      // Find the next biggest value (minimum value in the right branch)
-      // and replace current value node with that next biggest value.
-      const nextBiggerNode = nodeToRemove.right.findMin();
-      if (nextBiggerNode !== nodeToRemove.right) {
-        this.remove(nextBiggerNode.value);
-        nodeToRemove.value = nextBiggerNode.value;
-      } else {
-        // In case if next right value is the next bigger one and it doesn't have left child
-        // then just replace node that is going to be deleted with the right node.
-        nodeToRemove.value = nodeToRemove.right.value;
-        nodeToRemove.right = nodeToRemove.right.right;
-      }
-    } else {
-      // Node has only one child.
-      // Make this child to be a direct child of current node's parent.
-      if (nodeToRemove.left) {
-        parent.replaceChild(nodeToRemove, nodeToRemove.left);
-      } else {
-        parent.replaceChild(nodeToRemove, nodeToRemove.right);
-      }
-    }
+    return this.root.remove(value);
   }
 
   toString() {

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

@@ -47,6 +47,44 @@ export default class BinarySearchTreeNode extends BinaryTreeNode {
     return !!this.find(value);
   }
 
+  remove(value) {
+    const nodeToRemove = this.find(value);
+
+    if (!nodeToRemove) {
+      throw new Error('Item not found in the tree');
+    }
+
+    const { parent } = nodeToRemove;
+
+    if (!nodeToRemove.left && !nodeToRemove.right) {
+      // Node is a leaf and thus has no children.
+      // Just remove the pointer to this node from the parent node.
+      parent.removeChild(nodeToRemove);
+    } else if (nodeToRemove.left && nodeToRemove.right) {
+      // Node has two children.
+      // Find the next biggest value (minimum value in the right branch)
+      // and replace current value node with that next biggest value.
+      const nextBiggerNode = nodeToRemove.right.findMin();
+      if (nextBiggerNode !== nodeToRemove.right) {
+        this.remove(nextBiggerNode.value);
+        nodeToRemove.value = nextBiggerNode.value;
+      } else {
+        // In case if next right value is the next bigger one and it doesn't have left child
+        // then just replace node that is going to be deleted with the right node.
+        nodeToRemove.value = nodeToRemove.right.value;
+        nodeToRemove.right = nodeToRemove.right.right;
+      }
+    } else {
+      // Node has only one child.
+      // Make this child to be a direct child of current node's parent.
+      if (nodeToRemove.left) {
+        parent.replaceChild(nodeToRemove, nodeToRemove.left);
+      } else {
+        parent.replaceChild(nodeToRemove, nodeToRemove.right);
+      }
+    }
+  }
+
   findMin() {
     if (!this.left) {
       return this;

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

@@ -32,7 +32,7 @@ describe('BinarySearchTree', () => {
     expect(bst.contains(40)).toBeFalsy();
   });
 
-  it('should remove leaf nodes', () => {
+  it('should remove nodes', () => {
     const bst = new BinarySearchTree();
 
     bst.insert(10);
@@ -46,68 +46,4 @@ describe('BinarySearchTree', () => {
     bst.remove(20);
     expect(bst.toString()).toBe('10');
   });
-
-  it('should remove nodes with one child', () => {
-    const bst = new BinarySearchTree();
-
-    bst.insert(10);
-    bst.insert(20);
-    bst.insert(5);
-    bst.insert(30);
-
-    expect(bst.toString()).toBe('5,10,20,30');
-
-    bst.remove(20);
-    expect(bst.toString()).toBe('5,10,30');
-
-    bst.insert(1);
-    expect(bst.toString()).toBe('1,5,10,30');
-
-    bst.remove(5);
-    expect(bst.toString()).toBe('1,10,30');
-  });
-
-  it('should remove nodes with two children', () => {
-    const bst = new BinarySearchTree();
-
-    bst.insert(10);
-    bst.insert(20);
-    bst.insert(5);
-    bst.insert(30);
-    bst.insert(15);
-    bst.insert(25);
-
-    expect(bst.toString()).toBe('5,10,15,20,25,30');
-    expect(bst.root.find(20).left.value).toBe(15);
-    expect(bst.root.find(20).right.value).toBe(30);
-
-    bst.remove(20);
-    expect(bst.toString()).toBe('5,10,15,25,30');
-
-    bst.remove(15);
-    expect(bst.toString()).toBe('5,10,25,30');
-
-    bst.remove(10);
-    expect(bst.toString()).toBe('5,25,30');
-    expect(bst.root.value).toBe(25);
-
-    bst.remove(25);
-    expect(bst.toString()).toBe('5,30');
-
-    bst.remove(5);
-    expect(bst.toString()).toBe('30');
-  });
-
-  it('should throw error when trying to remove not existing node', () => {
-    const bst = new BinarySearchTree();
-
-    bst.insert(10);
-    bst.insert(20);
-
-    function removeNotExistingElementFromTree() {
-      bst.remove(30);
-    }
-
-    expect(removeNotExistingElementFromTree).toThrow();
-  });
 });

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

@@ -92,4 +92,83 @@ describe('BinarySearchTreeNode', () => {
     expect(node.find(5)).not.toBeNull();
     expect(node.find(5).value).toBe(5);
   });
+
+  it('should remove leaf nodes', () => {
+    const bstRootNode = new BinarySearchTreeNode();
+
+    bstRootNode.insert(10);
+    bstRootNode.insert(20);
+    bstRootNode.insert(5);
+
+    expect(bstRootNode.toString()).toBe('5,10,20');
+
+    bstRootNode.remove(5);
+    expect(bstRootNode.toString()).toBe('10,20');
+    bstRootNode.remove(20);
+    expect(bstRootNode.toString()).toBe('10');
+  });
+
+  it('should remove nodes with one child', () => {
+    const bstRootNode = new BinarySearchTreeNode();
+
+    bstRootNode.insert(10);
+    bstRootNode.insert(20);
+    bstRootNode.insert(5);
+    bstRootNode.insert(30);
+
+    expect(bstRootNode.toString()).toBe('5,10,20,30');
+
+    bstRootNode.remove(20);
+    expect(bstRootNode.toString()).toBe('5,10,30');
+
+    bstRootNode.insert(1);
+    expect(bstRootNode.toString()).toBe('1,5,10,30');
+
+    bstRootNode.remove(5);
+    expect(bstRootNode.toString()).toBe('1,10,30');
+  });
+
+  it('should remove nodes with two children', () => {
+    const bstRootNode = new BinarySearchTreeNode();
+
+    bstRootNode.insert(10);
+    bstRootNode.insert(20);
+    bstRootNode.insert(5);
+    bstRootNode.insert(30);
+    bstRootNode.insert(15);
+    bstRootNode.insert(25);
+
+    expect(bstRootNode.toString()).toBe('5,10,15,20,25,30');
+    expect(bstRootNode.find(20).left.value).toBe(15);
+    expect(bstRootNode.find(20).right.value).toBe(30);
+
+    bstRootNode.remove(20);
+    expect(bstRootNode.toString()).toBe('5,10,15,25,30');
+
+    bstRootNode.remove(15);
+    expect(bstRootNode.toString()).toBe('5,10,25,30');
+
+    bstRootNode.remove(10);
+    expect(bstRootNode.toString()).toBe('5,25,30');
+    expect(bstRootNode.value).toBe(25);
+
+    bstRootNode.remove(25);
+    expect(bstRootNode.toString()).toBe('5,30');
+
+    bstRootNode.remove(5);
+    expect(bstRootNode.toString()).toBe('30');
+  });
+
+  it('should throw error when trying to remove not existing node', () => {
+    const bstRootNode = new BinarySearchTreeNode();
+
+    bstRootNode.insert(10);
+    bstRootNode.insert(20);
+
+    function removeNotExistingElementFromTree() {
+      bstRootNode.remove(30);
+    }
+
+    expect(removeNotExistingElementFromTree).toThrow();
+  });
 });