diff --git a/README.md b/README.md
index b9c1787..a11001a 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
 # LeetCode
 
-## 問題: 
+## 問題: [104. Maximum Depth of Binary Tree](https://leetcode.com/problems/maximum-depth-of-binary-tree/description/)
 
 ## 前提
 
diff --git a/step1.md b/step1.md
index 54ebbc1..14eb34d 100644
--- a/step1.md
+++ b/step1.md
@@ -1,7 +1,76 @@
 # Step 1
 
+## Recursive DFS
+
+- base case: nodeがNoneのとき0を返す
+- recursive step: 左右のうちより深い方に1を足して返す
+
+```python
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution:
+    def maxDepth(self, root: Optional[TreeNode]) -> int:
+        if root is None:
+            return 0
+        return 1 + max(self.maxDepth(root.right), self.maxDepth(root.left))
+```
+
+時間計算量: O(n)
+
+空間計算量: O(n)
+
+## Iterative DFS
+
 ```python
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution:
+    def maxDepth(self, root: Optional[TreeNode]) -> int:
+        stack = [[root, 1]]
+        max_depth = 0
+        while stack:
+            node, depth = stack.pop()
+            if node:
+                max_depth = max(max_depth, depth)
+                stack.append([node.left, depth + 1])
+                stack.append([node.right, depth + 1])
+        return max_depth
 ```
-時間計算量:
 
-空間計算量:
+時間計算量: O(n)
+
+空間計算量: O(n)
+
+## BFS
+
+```python
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution:
+    def maxDepth(self, root: Optional[TreeNode]) -> int:
+        queue = deque([[root, 1]])
+        res = 0
+        while queue:
+            node, depth = queue.popleft()
+            if node:
+                res = depth
+                queue.append([node.left, depth + 1])
+                queue.append([node.right, depth + 1])
+        return res
+```
+
+時間計算量: O(n)
+
+空間計算量: O(n)
diff --git a/step2.md b/step2.md
index 6ec3360..bdf5af3 100644
--- a/step2.md
+++ b/step2.md
@@ -1,4 +1,21 @@
 # Step 2
 
 ```python
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution:
+    def maxDepth(self, root: Optional[TreeNode]) -> int:
+        queue = deque([[root, 1]])
+        res = 0
+        while queue:
+            node, depth = queue.popleft()
+            if node:
+                res = depth
+                queue.append([node.left, depth + 1])
+                queue.append([node.right, depth + 1])
+        return res
 ```
diff --git a/step3.md b/step3.md
index 522daa6..0e4966a 100644
--- a/step3.md
+++ b/step3.md
@@ -1,9 +1,29 @@
 # Step 3
 
+- dequeを書き慣れていないのでBFSでStep 3を行う
+
 ```python
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution:
+    def maxDepth(self, root: Optional[TreeNode]) -> int:
+        queue = deque([[root, 1]])
+        res = 0
+        while queue:
+            node, depth = queue.popleft()
+            if node:
+                res = depth
+                queue.append([node.left, depth + 1])
+                queue.append([node.right, depth + 1])
+        return res
 ```
-1回目: 分　秒
 
-2回目: 分　秒
+1回目: 1分　30秒
+
+2回目: 1分　33秒
 
-3回目: 分　秒
+3回目: 1分　32秒