From 2190c8b8ab9b2785ccb991431a70d39593e242f6 Mon Sep 17 00:00:00 2001
From: Kazuki Kitano <kitano-kazuki954@g.ecc.u-tokyo.ac.jp>
Date: Tue, 2 Jun 2026 10:41:43 +0900
Subject: [PATCH] step123

---
 memo.md | 113 +++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 112 insertions(+), 1 deletion(-)

diff --git a/memo.md b/memo.md
index efb0777..38d4a64 100644
--- a/memo.md
+++ b/memo.md
@@ -2,12 +2,123 @@
 
 ## アプローチ
 
+* `magazine`に含まれるワードを使って`ransomNote`が作れるならTrueを返す
+* `magazine`に含まれるワードの数分残機があって、`ransomNote`の各単語に遭遇するたびにそれを減らしていけばいいかな
+* `magazine`の長さをM
+* `ransomNote`の長さをNとすると
+* 計算量は, O(M + N)
+* 実行時間は, 10^5 * 2 / 10^6 ~= 0.1 sec程度
+* 使用メモリは,
+    * dictオブジェクトを作って, 文字の種類ごとに個数をカウントする
+    * intの28byteと, 文字の個数26個分程度かな？？
+    * 28 * 26 ~= 900 bytes
+* ここまで 3:21
+
 ## Code1-1
 
+* AC: 1:25
+
+```python
+import collections
+
+
+class Solution:
+    def canConstruct(self, ransomNote: str, magazine: str) -> bool:
+        char_to_count = collections.defaultdict(int)
+        for c in magazine:
+            char_to_count[c] += 1
+        
+        for c in ransomNote:
+            if c not in char_to_count:
+                return False
+            if char_to_count[c] == 0:
+                return False
+            char_to_count[c] -= 1
+        
+        return True
+                
+```
+
 # Step2
 
-## Code2-1
+## Code2-1 (Dict)
+
+* 変更なし
+
+```python
+import collections
+
+
+class Solution:
+    def canConstruct(self, ransomNote: str, magazine: str) -> bool:
+        char_to_count = collections.defaultdict(int)
+        for c in magazine:
+            char_to_count[c] += 1
+        
+        for c in ransomNote:
+            if c not in char_to_count:
+                return False
+            if char_to_count[c] == 0:
+                return False
+            char_to_count[c] -= 1
+        
+        return True
+
+```
+
+## Code2-2 (Counter)
+
+```python
+import collections
+
+
+class Solution:
+    def canConstruct(self, ransomNote: str, magazine: str) -> bool:
+        counter = collections.Counter(magazine)
+        for c in ransomNote:
+            if c not in counter:
+                return False
+            if counter[c] == 0:
+                return False
+            counter[c] -= 1
+        return True
+                
+```
+
+## 他の人のPRを見る
+
+* https://github.com/tom4649/Coding/pull/66
+    * 方針は同じ
+    * `dict.get()`を使うことで, `if c not in dict`と`if dict[c] == 0`を同時に判定できる
+    * 制約で英語小文字だけであることから, 長さ26の配列を用意してもいい
+* https://github.com/ryosuketc/leetcode_grind75/pull/15
+* https://github.com/huyfififi/coding-challenges/pull/15
 
 # Step3
 
 ## Code3-1
+
+* 1st: 0:48
+* 2nd: 0:31
+* 3rd: 0:31
+
+* そもそもdefaultdict使っているから, `char_to_count.get(c, 0)`としなくていい
+
+```python
+import collections
+
+
+class Solution:
+    def canConstruct(self, ransomNote: str, magazine: str) -> bool:
+        char_to_count = collections.defaultdict(int)
+        for c in magazine:
+            char_to_count[c] += 1
+        
+        for c in ransomNote:
+            if char_to_count[c] == 0:
+                return False
+            char_to_count[c] -= 1
+        
+        return True
+
+```
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