diff --git a/invert-binary-tree/taewanseoul.ts b/invert-binary-tree/taewanseoul.ts
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+/**
+ * 226. Invert Binary Tree
+ * Given the root of a binary tree, invert the tree, and return its root.
+ *
+ * https://leetcode.com/problems/invert-binary-tree/description/
+ *
+ */
+
+class TreeNode {
+  val: number;
+  left: TreeNode | null;
+  right: TreeNode | null;
+  constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
+    this.val = val === undefined ? 0 : val;
+    this.left = left === undefined ? null : left;
+    this.right = right === undefined ? null : right;
+  }
+}
+
+// O(n) time
+// O(n) space
+function invertTree(root: TreeNode | null): TreeNode | null {
+  if (!root) {
+    return null;
+  }
+
+  const left = invertTree(root.left);
+  const right = invertTree(root.right);
+
+  root.left = right;
+  root.right = left;
+
+  return root;
+}