diff --git a/CS notes/pages/Leetcode Binary-Tree-Inorder-Traversal.md b/CS notes/pages/Leetcode Binary-Tree-Inorder-Traversal.md
index 3bca0db..13e4d5a 100644
--- a/CS notes/pages/Leetcode Binary-Tree-Inorder-Traversal.md	
+++ b/CS notes/pages/Leetcode Binary-Tree-Inorder-Traversal.md	
@@ -94,5 +94,40 @@ public:
 
 Iteration
 ```cpp
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left),
+ * right(right) {}
+ * };
+ */
+class Solution {
+public:
+  vector<int> inorderTraversal(TreeNode *root) {
+    // Iteration
+    stack<TreeNode *> pending;
+    vector<int> answer;
+
+    while (root || !pending.empty()) {
+      // traverse left first.
+      while (root) {
+        pending.push(root);
+        root = root->left;
+      }
+
+      root = pending.top();
+      pending.pop();
+      answer.push_back(root->val);
+      root = root->right;
+    }
+
+    return answer;
+  }
+};
 
 ```
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