From 6af7639f6d4f7512932e6fc8fa134e17c72bcb20 Mon Sep 17 00:00:00 2001
From: Rytxxx <k.ryuto.5@icloud.com>
Date: Tue, 6 Jan 2026 21:38:33 -0800
Subject: [PATCH 1/2] 2-add-two-numbers

---
 2-add-two-numbers/memo.md  | 13 +++++++++++++
 2-add-two-numbers/steo2.py | 28 ++++++++++++++++++++++++++++
 2-add-two-numbers/step1.py | 25 +++++++++++++++++++++++++
 2-add-two-numbers/step3.py | 30 ++++++++++++++++++++++++++++++
 4 files changed, 96 insertions(+)
 create mode 100644 2-add-two-numbers/memo.md
 create mode 100644 2-add-two-numbers/steo2.py
 create mode 100644 2-add-two-numbers/step1.py
 create mode 100644 2-add-two-numbers/step3.py

diff --git a/2-add-two-numbers/memo.md b/2-add-two-numbers/memo.md
new file mode 100644
index 0000000..1777c4d
--- /dev/null
+++ b/2-add-two-numbers/memo.md
@@ -0,0 +1,13 @@
+## step1で考えたこと
+
+和が10以上になった時にどう繰り上げを行うか。
+
+dummyというか結果を格納するList Nodeは必要そう
+
+module 10 でのあまりをNodeの値として使えそう
+
+## step1を振り返って
+問題を解く方針はだいたいあっていたが、コードの細かい書き方や、まだLinked Listの書き方がイマイチになっていることに気づいた。
+
+今回の場合、和の一の位の数をNodeの後ろにどんどん追加していく必要があるからtailを使う.  
+もし、問題の特性が、Nodeを前に前に追加していく場合だと、今度はtailではなくheadを使って操作していく。
\ No newline at end of file
diff --git a/2-add-two-numbers/steo2.py b/2-add-two-numbers/steo2.py
new file mode 100644
index 0000000..97e2174
--- /dev/null
+++ b/2-add-two-numbers/steo2.py
@@ -0,0 +1,28 @@
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+class Solution:
+    def addTwoNumbers(self, l1: Optional[ListNode], l2: Optional[ListNode]) -> Optional[ListNode]:
+        result = ListNode(0)
+        tail = result
+        list1 = l1
+        list2 = l2
+        carry = 0
+
+        while list1 or list2 or carry:
+            x = list1.val if list1 else 0
+            y = list2.val if list2 else 0
+            
+            total = x + y + carry
+            carry = total // 10
+            digit = total % 10
+
+            tail.next = ListNode(digit)
+            tail = tail.next
+            if list1:
+                list1 = list1.next
+            if list2:
+                list2 = list2.next
+        return result.next
\ No newline at end of file
diff --git a/2-add-two-numbers/step1.py b/2-add-two-numbers/step1.py
new file mode 100644
index 0000000..be7db01
--- /dev/null
+++ b/2-add-two-numbers/step1.py
@@ -0,0 +1,25 @@
+# 動かないコード
+
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+class Solution:
+    def addTwoNumbers(self, l1: Optional[ListNode], l2: Optional[ListNode]) -> Optional[ListNode]:
+        result = ListNode(0, l1)
+        list1 = l1.val
+        list2 = l2.val
+        res = 0
+
+        while list1 or list2:
+            if res > 10:
+                res = list1.val + list2.val + 1
+            else:
+                res = list1.val + list2.val
+            if res >= 10:
+                result.next = res % 10
+            else: result.next = res
+            list1 = list1.next
+            list2 = list2.next
+        return result.next
\ No newline at end of file
diff --git a/2-add-two-numbers/step3.py b/2-add-two-numbers/step3.py
new file mode 100644
index 0000000..2ea40f8
--- /dev/null
+++ b/2-add-two-numbers/step3.py
@@ -0,0 +1,30 @@
+# step2のコードをもう少し簡潔に書いたVersion
+
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+class Solution:
+    def addTwoNumbers(self, l1: Optional[ListNode], l2: Optional[ListNode]) -> Optional[ListNode]:
+        dummy = ListNode()
+        res = dummy
+
+        total = carry = 0
+
+        while l1 or l2 or carry:
+            total = carry
+
+            if l1:
+                total += l1.val
+                l1 = l1.next
+            if l2:
+                total += l2.val
+                l2 = l2.next
+
+            digit = total % 10
+            carry = total // 10
+            dummy.next = ListNode(digit)
+            dummy = dummy.next
+
+        return res.next
\ No newline at end of file

From a108d47314b0187c246a7d71f28e2f0095e1c90c Mon Sep 17 00:00:00 2001
From: Rytxxx <k.ryuto.5@icloud.com>
Date: Fri, 9 Jan 2026 13:58:37 -0800
Subject: [PATCH 2/2] fix: way to move pointer

---
 2-add-two-numbers/step3.py | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/2-add-two-numbers/step3.py b/2-add-two-numbers/step3.py
index 2ea40f8..154ec91 100644
--- a/2-add-two-numbers/step3.py
+++ b/2-add-two-numbers/step3.py
@@ -8,7 +8,7 @@
 class Solution:
     def addTwoNumbers(self, l1: Optional[ListNode], l2: Optional[ListNode]) -> Optional[ListNode]:
         dummy = ListNode()
-        res = dummy
+        node = dummy
 
         total = carry = 0
 
@@ -24,7 +24,7 @@ def addTwoNumbers(self, l1: Optional[ListNode], l2: Optional[ListNode]) -> Optio
 
             digit = total % 10
             carry = total // 10
-            dummy.next = ListNode(digit)
-            dummy = dummy.next
+            node.next = ListNode(digit)
+            node = node.next
 
-        return res.next
\ No newline at end of file
+        return dummy.next
\ No newline at end of file