diff --git a/0104-maximum-depth-of-binary-tree/memo.md b/0104-maximum-depth-of-binary-tree/memo.md
new file mode 100644
index 0000000..5dc1f44
--- /dev/null
+++ b/0104-maximum-depth-of-binary-tree/memo.md
@@ -0,0 +1,11 @@
+### step1
+
+わからなかったのでChatGPTに解いてもらった。DFSで左右のnodeのうち深い方を取って+1していくことを繰り返すだけだった。
+
+### step2
+
+変更点なし。
+
+### step3
+
+3回通すまで書き直し。
diff --git a/0104-maximum-depth-of-binary-tree/step1.cpp b/0104-maximum-depth-of-binary-tree/step1.cpp
new file mode 100644
index 0000000..824f313
--- /dev/null
+++ b/0104-maximum-depth-of-binary-tree/step1.cpp
@@ -0,0 +1,13 @@
+class Solution {
+public:
+    int maxDepth(TreeNode* root) {
+        if (root == nullptr) {
+            return 0;
+        }
+
+        int leftDepth = maxDepth(root->leftNode);
+        int rightDepth = maxDepth(root->rightNode);
+
+        return max(leftDepth, rightDepth) + 1;
+    }
+};
diff --git a/0104-maximum-depth-of-binary-tree/step2.cpp b/0104-maximum-depth-of-binary-tree/step2.cpp
new file mode 100644
index 0000000..824f313
--- /dev/null
+++ b/0104-maximum-depth-of-binary-tree/step2.cpp
@@ -0,0 +1,13 @@
+class Solution {
+public:
+    int maxDepth(TreeNode* root) {
+        if (root == nullptr) {
+            return 0;
+        }
+
+        int leftDepth = maxDepth(root->leftNode);
+        int rightDepth = maxDepth(root->rightNode);
+
+        return max(leftDepth, rightDepth) + 1;
+    }
+};
diff --git a/0104-maximum-depth-of-binary-tree/step3.cpp b/0104-maximum-depth-of-binary-tree/step3.cpp
new file mode 100644
index 0000000..824f313
--- /dev/null
+++ b/0104-maximum-depth-of-binary-tree/step3.cpp
@@ -0,0 +1,13 @@
+class Solution {
+public:
+    int maxDepth(TreeNode* root) {
+        if (root == nullptr) {
+            return 0;
+        }
+
+        int leftDepth = maxDepth(root->leftNode);
+        int rightDepth = maxDepth(root->rightNode);
+
+        return max(leftDepth, rightDepth) + 1;
+    }
+};