From 65496d0cd426cba00d919c208e77b586bd8d9a01 Mon Sep 17 00:00:00 2001
From: kazukiii <kazumatsu.dev28@gmail.com>
Date: Mon, 10 Jun 2024 16:14:38 -0700
Subject: [PATCH 1/2] =?UTF-8?q?step1,=20step2,=20step3=E3=82=92=E8=BF=BD?=
 =?UTF-8?q?=E5=8A=A0?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 arai60/valid-parentheses/README.md | 22 ++++++++++++++++++++++
 arai60/valid-parentheses/step1.py  | 22 ++++++++++++++++++++++
 arai60/valid-parentheses/step2.py  | 20 ++++++++++++++++++++
 arai60/valid-parentheses/step3.py  | 20 ++++++++++++++++++++
 4 files changed, 84 insertions(+)
 create mode 100644 arai60/valid-parentheses/README.md
 create mode 100644 arai60/valid-parentheses/step1.py
 create mode 100644 arai60/valid-parentheses/step2.py
 create mode 100644 arai60/valid-parentheses/step3.py

diff --git a/arai60/valid-parentheses/README.md b/arai60/valid-parentheses/README.md
new file mode 100644
index 0000000..08e51e8
--- /dev/null
+++ b/arai60/valid-parentheses/README.md
@@ -0,0 +1,22 @@
+## 考察
+- 過去に解いたことあり
+- 方針
+    - stackを使って対応を見ていく
+        - 前から文字を見ていって、open bracketが来たらstackに積む
+        - close bracketが来たら、stackから要素をpopして対応をチェックする(stackが空じゃないかだけ注意)
+        - 最後にstackが空になっていたらOK
+        - time: O(n), space: O(n)
+- あとは実装
+
+## Step1
+- 上のアルゴリズムを実装
+- time: O(n), space: O(n)
+
+## Step2
+- 手続き的にbracketの対応関係を判定していた箇所を、辞書を使って宣言的な記述に変更
+    - 結果、余計なif文がかなり減った
+
+## Step3
+- 1回目: 1m51s
+- 2回目: 1m53s
+- 3回目: 1m28s
diff --git a/arai60/valid-parentheses/step1.py b/arai60/valid-parentheses/step1.py
new file mode 100644
index 0000000..b99671b
--- /dev/null
+++ b/arai60/valid-parentheses/step1.py
@@ -0,0 +1,22 @@
+class Solution:
+    def isValid(self, s: str) -> bool:
+        stack = []
+        for c in s:
+            if c in ['(', '{', '[']:
+                stack.append(c)
+            else:
+                if not stack:
+                    return False
+
+                open_bracket = stack.pop()
+                if c == ')':
+                    if not open_bracket == '(':
+                        return False
+                elif c == '}':
+                    if not open_bracket == '{':
+                        return False
+                else:
+                    if not open_bracket == '[':
+                        return False
+
+        return not stack
diff --git a/arai60/valid-parentheses/step2.py b/arai60/valid-parentheses/step2.py
new file mode 100644
index 0000000..e5787a1
--- /dev/null
+++ b/arai60/valid-parentheses/step2.py
@@ -0,0 +1,20 @@
+class Solution:
+    def isValid(self, s: str) -> bool:
+        stack = []
+        bracket_pairs = {
+            '(': ')',
+            '{': '}',
+            '[': ']',
+        }
+        for c in s:
+            if c in bracket_pairs:
+                stack.append(c)
+            else:
+                if not stack:
+                    return False
+
+                open_bracket = stack.pop()
+                if not bracket_pairs[open_bracket] == c:
+                    return False
+
+        return not stack
diff --git a/arai60/valid-parentheses/step3.py b/arai60/valid-parentheses/step3.py
new file mode 100644
index 0000000..e5787a1
--- /dev/null
+++ b/arai60/valid-parentheses/step3.py
@@ -0,0 +1,20 @@
+class Solution:
+    def isValid(self, s: str) -> bool:
+        stack = []
+        bracket_pairs = {
+            '(': ')',
+            '{': '}',
+            '[': ']',
+        }
+        for c in s:
+            if c in bracket_pairs:
+                stack.append(c)
+            else:
+                if not stack:
+                    return False
+
+                open_bracket = stack.pop()
+                if not bracket_pairs[open_bracket] == c:
+                    return False
+
+        return not stack

From a9ff7d4c80acda85ac04d41d2333121b257337b3 Mon Sep 17 00:00:00 2001
From: kazukiii <kazumatsu.dev28@gmail.com>
Date: Tue, 11 Jun 2024 13:54:47 -0700
Subject: [PATCH 2/2] =?UTF-8?q?step4=E3=82=92=E8=BF=BD=E5=8A=A0?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 arai60/valid-parentheses/README.md | 11 +++++++++++
 arai60/valid-parentheses/step4.py  | 21 +++++++++++++++++++++
 2 files changed, 32 insertions(+)
 create mode 100644 arai60/valid-parentheses/step4.py

diff --git a/arai60/valid-parentheses/README.md b/arai60/valid-parentheses/README.md
index 08e51e8..7009261 100644
--- a/arai60/valid-parentheses/README.md
+++ b/arai60/valid-parentheses/README.md
@@ -20,3 +20,14 @@
 - 1回目: 1m51s
 - 2回目: 1m53s
 - 3回目: 1m28s
+
+## Step4
+- レビューを元にコードを修正
+- 変数名の見直し
+    - stack -> bracket_stack
+        - 何を入れるstackなのかを明確に
+    - bracket_pairs -> open_to_close
+        - 例えば、open_to_close[open_bracket] という記述を見たときにclose_bracketが返ってくることが一目でわかる
+        - より具体的になって、わかりやすくなった感覚
+- `if not open_to_close[open_bracket] == c:` と書いていたところを `if open_to_close[open_bracket] != c:`に
+- early continueしてネストを浅く
diff --git a/arai60/valid-parentheses/step4.py b/arai60/valid-parentheses/step4.py
new file mode 100644
index 0000000..4fa6a73
--- /dev/null
+++ b/arai60/valid-parentheses/step4.py
@@ -0,0 +1,21 @@
+class Solution:
+    def isValid(self, s: str) -> bool:
+        bracket_stack = []
+        open_to_close = {
+            '(': ')',
+            '{': '}',
+            '[': ']',
+        }
+        for c in s:
+            if c in open_to_close:
+                bracket_stack.append(c)
+                continue
+
+            if not bracket_stack:
+                return False
+
+            open_bracket = bracket_stack.pop()
+            if open_to_close[open_bracket] != c:
+                return False
+
+        return not bracket_stack