problem: new problem solution - 226 . Invert Binary Tree

README.md

@@ -107,6 +107,7 @@ My approach to solving LeetCode problems typically involves the following steps:
 | 144  | [Binary Tree Preorder Traversal](https://leetcode.com/problems/binary-tree-preorder-traversal/)                                                   | Algorithms | [TypeScript](./problems/algorithms/binaryTreePreorderTraversal/BinaryTreePreorderTraversal.ts)                                           | Easy       |
 | 145  | [Binary Tree Postorder Traversal](https://leetcode.com/problems/binary-tree-postorder-traversal/)                                                 | Algorithms | [TypeScript](./problems/algorithms/binaryTreePostorderTraversal/BinaryTreePostorderTraversal.ts)                                         | Easy       |
 | 222  | [Count Complete Tree Nodes](https://leetcode.com/problems/count-complete-tree-nodes/)                                                             | Algorithms | [TypeScript](./problems/algorithms/countCompleteTreeNodes/CountCompleteTreeNodes.ts)                                                     | Easy       |
+| 226  | [Invert Binary Tree](https://leetcode.com/problems/invert-binary-tree/)                                                                           | Algorithms | [TypeScript](./problems/algorithms/invertBinaryTree/InvertBinaryTree.ts)                                                                 | Easy       |
 | ...  | ...                                                                                                                                               | ...        | ...                                                                                                                                      | ...        |
 
 In this table:

problems/algorithms/invertBinaryTree/InvertBinaryTree.test.ts

@@ -0,0 +1,55 @@
+// Source : https://leetcode.com/problems/invert-binary-tree/
+// Author : Francisco Tomas
+// Date   : 2023-11-22
+
+import { invertTree, NodeTree } from "./InvertBinaryTree";
+
+describe("invertTree", () => {
+  test("invert empty binary tree", () => {
+    const result = invertTree(null);
+    expect(result).toBe(null);
+  });
+
+  test("invert binary tree with few elements", () => {
+    const result = invertTree(
+      new NodeTree(2, new NodeTree(1, null, null), new NodeTree(3, null, null)),
+    );
+    expect(result).toStrictEqual(
+      new NodeTree(2, new NodeTree(3, null, null), new NodeTree(1, null, null)),
+    );
+  });
+
+  test("invert slighty bigger binary tree", () => {
+    const result = invertTree(
+      new NodeTree(
+        4,
+        new NodeTree(
+          2,
+          new NodeTree(1, null, null),
+          new NodeTree(3, null, null),
+        ),
+        new NodeTree(
+          7,
+          new NodeTree(6, null, null),
+          new NodeTree(9, null, null),
+        ),
+      ),
+    );
+
+    expect(result).toStrictEqual(
+      new NodeTree(
+        4,
+        new NodeTree(
+          7,
+          new NodeTree(9, null, null),
+          new NodeTree(6, null, null),
+        ),
+        new NodeTree(
+          2,
+          new NodeTree(3, null, null),
+          new NodeTree(1, null, null),
+        ),
+      ),
+    );
+  });
+});

problems/algorithms/invertBinaryTree/InvertBinaryTree.ts

@@ -0,0 +1,78 @@
+// Source : https://leetcode.com/problems/invert-binary-tree/
+// Author : Francisco Tomas
+// Date   : 2023-11-22
+
+/*****************************************************************************************************
+ *
+ * Given the root of a binary tree, invert the tree, and return its root.
+ *
+ * Example 1:
+ *
+ * Input: root = [4,2,7,1,3,6,9]
+ * Output: [4,7,2,9,6,3,1]
+ *
+ * Example 2:
+ *
+ * Input: root = [2,1,3]
+ * Output: [2,3,1]
+ *
+ * Example 3:
+ *
+ * Input: root = []
+ * Output: []
+ *
+ * Constraints:
+ *
+ * 	The number of nodes in the tree is in the range [0, 100].
+ * 	-100 <= Node.val <= 100
+ ******************************************************************************************************/
+
+type BT = NodeTree | null;
+export class NodeTree {
+  val: number;
+  left: BT;
+  right: BT;
+  constructor(val?: number, left?: BT, right?: BT) {
+    this.val = val ?? 0;
+    this.left = left === undefined ? null : left;
+    this.right = right === undefined ? null : right;
+  }
+}
+
+/**
+ * BT -> BT
+ * given the root of a binary tree, invert the tree, and return its root
+
+ * Stub:
+ function invertTree(root: BT): BT {return null}
+
+ * Tests:
+ * I: root = [4,2,7,1,3,6,9] -> O: [4,7,2,9,6,3,1]
+ * I: root = [2,1,3] -> O: [2,3,1]
+ * I: root = [] -> O: []
+
+ * Template:
+ function invertTree(root: BT): BT {
+     if (root === null) {return null}
+     else {
+         return (... root.val
+                     (invertTree(root.left))
+                     (invertTree(root.right)))
+     }
+ }
+
+ * CONSTRAINTS:
+ * - The number of nodes in the tree is in the range [0, 100].
+ * - -100 <= Node.val <= 100
+ */
+export function invertTree(root: BT): BT {
+  if (root === null) {
+    return null;
+  } else {
+    return new NodeTree(
+      root.val,
+      invertTree(root.right),
+      invertTree(root.left),
+    );
+  }
+}