diff --git a/209.Minimum-Size-Subarray-Sum/memo.md b/209.Minimum-Size-Subarray-Sum/memo.md
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+# 209. Minimum Size Subarray Sum
+
+-　sol1.py: 何も見ないで書いた。sliding windowで解ける。O(n)。
+
+https://github.com/SuperHotDogCat/coding-interview/pull/31/changes
+
+二重のwhile文で書いている。rightの始まりと終わりは確定しているので、個人的にはfor文が良いのではないかと思った。
+min_length = len(nums) + 1とするのはなるほど。ただ分かりやすさではinfでも悪くはないと思う。
+
+https://github.com/olsen-blue/Arai60/pull/50/changes/BASE..1b460a0c97f2ef17efe579db6835cb0623d6cf67#diff-6d4eb2707ed57d8037bfa2e5985424b237a407741a7602ba92b31e090d1cb096
+
+https://github.com/naoto-iwase/leetcode/pull/50
+
+二分探索と分割統治法で書く。計算量はO(nlogn)になる
+二分探索 -> 自分で書くと、leftのindexの処理が彼と異なった。leftを含めるか否か。
+
+二分探索の方は自分でも思いついただろう（今回は人の答えを見たが）
+分割統治法は人のを見て初めて気づいたので、頭に入れておきたい
+
+
+
diff --git a/209.Minimum-Size-Subarray-Sum/sol1.py b/209.Minimum-Size-Subarray-Sum/sol1.py
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+import math
+
+
+class Solution:
+    def minSubArrayLen(self, target: int, nums: List[int]) -> int:
+        left = 0
+        current_sum = 0
+        min_subarray_len = float("inf")
+        for right, num_right in enumerate(nums):
+            current_sum += num_right
+            if current_sum < target:
+                continue
+            while left < len(nums) and current_sum - nums[left] >= target:
+                current_sum -= nums[left]
+                left += 1
+            min_subarray_len = min(min_subarray_len, right - left + 1)
+
+        return 0 if math.isinf(min_subarray_len) else min_subarray_len
diff --git a/209.Minimum-Size-Subarray-Sum/sol2.py b/209.Minimum-Size-Subarray-Sum/sol2.py
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+++ b/209.Minimum-Size-Subarray-Sum/sol2.py
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+import itertools
+import bisect
+import math
+
+
+class Solution:
+    def minSubArrayLen(self, target: int, nums: List[int]) -> int:
+        left = 0
+        min_subarray_len = float("inf")
+        prefix_sum = list(itertools.accumulate(nums))
+        for left, num_left in enumerate(nums):
+            right = bisect.bisect_left(prefix_sum, target + prefix_sum[left] - num_left)
+            if right < len(nums):
+                min_subarray_len = min(min_subarray_len, right - left + 1)
+        return 0 if math.isinf(min_subarray_len) else min_subarray_len
diff --git a/209.Minimum-Size-Subarray-Sum/sol3.py b/209.Minimum-Size-Subarray-Sum/sol3.py
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+++ b/209.Minimum-Size-Subarray-Sum/sol3.py
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+import math
+
+
+class Solution:
+    def minSubArrayLen(self, target: int, nums: List[int]) -> int:
+        def devide_and_conquer(left, right):
+            if left > right:
+                return float("inf")
+            if left == right:
+                return float("inf") if nums[left] < target else 1
+            mid = left + (right - left) // 2
+            return min(
+                devide_and_conquer(left, mid),
+                devide_and_conquer(mid + 1, right),
+                cross_middle(left, right, mid, target),
+            )
+
+        def cross_middle(left, right, mid, target):
+            if mid >= len(nums):
+                return float("inf")
+            left_cross = mid
+            right_cross = mid + 1
+            min_length = float("inf")
+            current_sum = nums[left_cross] + nums[right_cross]
+            while right_cross <= right:
+                while current_sum < target and left_cross > left:
+                    left_cross -= 1
+                    current_sum += nums[left_cross]
+                if current_sum >= target:
+                    min_length = min(min_length, right_cross - left_cross + 1)
+                right_cross += 1
+                if right_cross > right:
+                    continue
+                current_sum += nums[right_cross]
+                while current_sum >= target and left_cross < mid:
+                    current_sum -= nums[left_cross]
+                    left_cross += 1
+
+            return min_length
+
+        min_length = devide_and_conquer(0, len(nums) - 1)
+        return 0 if math.isinf(min_length) else min_length