617. Merge Two Binary Trees

README.md

@@ -1,6 +1,6 @@
 # LeetCode
 
-## 問題: [Link Text](URL)
+## 問題: [617. Merge Two Binary Trees](https://leetcode.com/problems/merge-two-binary-trees/description/)
 
 ## 前提
 

step1.md

@@ -1,7 +1,35 @@
 # Step 1
 
+- non-tail recursionでできると思うが上手く言語化できない。
+
 ```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 mergeTrees(self, root1: Optional[TreeNode], root2: Optional[TreeNode]) -> Optional[TreeNode]:
+        if root1 is None and root2 is None:
+            return None
+        if root1 is None:
+            merged_root = TreeNode(val=root2.val)
+            merged_root.left = self.mergeTrees(None, root2.left)
+            merged_root.right = self.mergeTrees(None, root2.right)
+        elif root2 is None:
+            merged_root = TreeNode(val=root1.val)
+            merged_root.left = self.mergeTrees(root1.left, None)
+            merged_root.right = self.mergeTrees(root1.right, None)
+        else:
+            merged_root = TreeNode(val=root1.val+root2.val)
+            merged_root.left = self.mergeTrees(root1.left, root2.left)
+            merged_root.right = self.mergeTrees(root1.right, root2.right)
+        return merged_root
 ```
-時間計算量:
 
-空間計算量:
+時間計算量: O(n)
+
+空間計算量: O(n)
+
+- 何も見ずに書けたものの、30分くらいかかってしまった。

step2.md

@@ -1,4 +1,23 @@
 # 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 mergeTrees(self, root1: Optional[TreeNode], root2: Optional[TreeNode]) -> Optional[TreeNode]:
+        if not root1 and not root2:
+            return None
+
+        val1 = root1.val if root1 else 0
+        val2 = root2.val if root2 else 0
+        merged_root = TreeNode(val1 + val2)
+
+        merged_root.left = self.mergeTrees(root1.left if root1 else None, root2.left if root2 else None)
+        merged_root.right = self.mergeTrees(root1.right if root1 else None, root2.right if root2 else None)
+
+        return merged_root
 ```

step3.md

@@ -1,9 +1,29 @@
 # Step 3
 
 ```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 mergeTrees(self, root1: Optional[TreeNode], root2: Optional[TreeNode]) -> Optional[TreeNode]:
+        if not root1 and not root2:
+            return None
+
+        val1 = root1.val if root1 else 0
+        val2 = root2.val if root2 else 0
+        merged_root = TreeNode(val1 + val2)
+
+        merged_root.left = self.mergeTrees(root1.left if root1 else None, root2.left if root2 else None)
+        merged_root.right = self.mergeTrees(root1.right if root1 else None, root2.right if root2 else None)
+
+        return merged_root
 ```
-1回目: 分　秒
 
-2回目: 分　秒
+1回目: 3分　7秒
+
+2回目: 3分　8秒
 
-3回目: 分　秒
+3回目: 3分　9秒