Added invert binary tree solution

Author: nhistory

invert-binary-tree/nhistory.js

@@ -0,0 +1,26 @@
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @return {TreeNode}
+ */
+var invertTree = function (root) {
+  // Check root is null
+  if (!root) return null;
+  // Create left and right variable to make recurrsive
+  let left = root.left;
+  let right = root.right;
+  // Execute invertTree functino
+  root.left = invertTree(right);
+  root.right = invertTree(left);
+  return root;
+};
+
+// TC: O(n)
+// SC: O(n)