diff --git a/53/memo.md b/53/memo.md
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+# 53. Maximum Subarray
+
+- 愚直にsol1.pyを書いた
+    - 計算量 O(n)
+- Kadaneのアルゴリズム
+    - https://en.wikipedia.org/wiki/Maximum_subarray_problem
+    - https://qiita.com/awesam/items/37a0ceb1468feef3a403
+    - https://ark4rk.hatenablog.com/entry/2018/01/08/002508
+    -  自然言語で説明すれば、「arrayを一巡し、各要素(a_iとする)で終わるものが最大値になりうるかを検証する。一つ前の要素で終わったsubarrayの最大値を記録しておけば、それにa_iを加えたものかa_iだけのsubarrayがa_iで終わったarrayの最大値である」
+    - sol2.py
+- https://discord.com/channels/1084280443945353267/1206101582861697046/1207518775851876362
+    - sol1.pyと同じ考え
+- https://github.com/mamo3gr/arai60/blob/53_maximum-subarray/53_maximum-subarray/step1.py
+    - cumulative sumって配列の最初からではなくてもそう呼ぶのかな
+- https://github.com/mamo3gr/arai60/blob/53_maximum-subarray/53_maximum-subarray/step3.py
+    - > マイナスなら相続をやめる
+- https://github.com/mamo3gr/arai60/blob/53_maximum-subarray/53_maximum-subarray/step2.py
+    - 分割統治法, O(Nlog N)
+
+
diff --git a/53/sol1.py b/53/sol1.py
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+class Solution:
+    def maxSubArray(self, nums: List[int]) -> int:
+        max_sum = -float("inf")
+        cumulative_sum = 0
+        min_cumulative_sum = 0
+        for n in nums:
+            cumulative_sum += n
+            max_sum = max(max_sum, cumulative_sum - min_cumulative_sum)
+            min_cumulative_sum = min(min_cumulative_sum, cumulative_sum)
+
+        return max_sum
diff --git a/53/sol2.py b/53/sol2.py
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+class Solution:
+    def maxSubArray(self, nums: List[int]) -> int:
+        max_so_far = -float("inf")
+        max_ending_with_n = -float("inf")
+        for n in nums:
+            max_ending_with_n = max(n, max_ending_with_n + n)
+            max_so_far = max(max_so_far, max_ending_with_n)
+
+        return max_so_far