209. Minimum Size Subarray Sum

209_minimum-size-subarray-sum.md

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+# 209. Minimum Size Subarray Sum
+
+## 1st
+
+### ①
+
+右端をループで回しながら、subarray_sum < target となるまで左端を進める、を繰り返す。
+
+所要時間: 8:15
+
+n: len(nums)
+- 時間計算量: O(n)
+- 空間計算量: O(n)
+
+```py
+class Solution:
+    def minSubArrayLen(self, target: int, nums: List[int]) -> int:
+        assert target > 0
+        left = -1 # exclusive
+        subarray_sum = 0
+        min_length = len(nums) + 1
+        for right in range(len(nums)):
+            subarray_sum += nums[right]
+            while subarray_sum >= target:
+                min_length = min(min_length, right - left)
+                left += 1
+                subarray_sum -= nums[left]
+        if min_length == len(nums) + 1:
+            return 0
+        return min_length
+```
+
+### ②
+
+左端をループで回すパターン。
+
+所要時間: 16:45
+
+n: len(nums)
+- 時間計算量: O(n)
+- 空間計算量: O(n)
+
+```py
+class Solution:
+    def minSubArrayLen(self, target: int, nums: List[int]) -> int:
+        min_length = len(nums) + 1
+        subarray_sum = 0
+        end = 0
+        for begin in range(len(nums)):
+            while end < len(nums) and subarray_sum < target:
+                subarray_sum += nums[end]
+                end += 1
+            if subarray_sum >= target:
+                min_length = min(min_length, end - begin)
+            subarray_sum -= nums[begin]
+        if min_length == len(nums) + 1:
+            return 0
+        return min_length
+```
+
+## 2nd
+
+### 参考
+
+- https://discord.com/channels/1084280443945353267/1233603535862628432/1264033965724012656
+  - https://github.com/goto-untrapped/Arai60/pull/40
+
+累積和を使ってもよい。
+
+```py
+class Solution:
+    def minSubArrayLen(self, target: int, nums: List[int]) -> int:
+        assert target > 0
+        cumsum = [0]
+        for num in nums:
+            cumsum.append(cumsum[-1] + num)
+        begin = 0
+        min_length = len(nums) + 1
+        for end in range(len(cumsum)):
+            while cumsum[end] - cumsum[begin] >= target:
+                min_length = min(min_length, end - begin)
+                begin += 1
+        if min_length == len(nums) + 1:
+            return 0
+        return min_length
+```
+
+- https://discord.com/channels/1084280443945353267/1225849404037009609/1253024249040474258
+  - https://github.com/SuperHotDogCat/coding-interview/pull/31
+- https://discord.com/channels/1084280443945353267/1196472827457589338/1246777474927562752
+  - https://github.com/Mike0121/LeetCode/pull/22
+
+累積和と二分探索。
+
+```py
+class Solution:
+    def minSubArrayLen(self, target: int, nums: List[int]) -> int:
+        cumsum = [0]
+        for num in nums:
+            cumsum.append(cumsum[-1] + num)
+        min_length = len(nums) + 1
+        for i in range(len(cumsum)):
+            j = bisect_left(cumsum, cumsum[i] + target)
+            if j < len(cumsum):
+                min_length = min(min_length, j - i)
+        if min_length == len(nums) + 1:
+            return 0
+        return min_length
+```
+
+- https://discord.com/channels/1084280443945353267/1201211204547383386/1228603635693387808
+  - https://github.com/shining-ai/leetcode/pull/49
+- https://discord.com/channels/1084280443945353267/1200089668901937312/1219219869510140005
+  - https://github.com/hayashi-ay/leetcode/pull/51
+
+全探索。TLE。
+
+```py
+class Solution:
+    def minSubArrayLen(self, target: int, nums: List[int]) -> int:
+        min_length = len(nums) + 1
+        for begin in range(len(nums)):
+            subarray_sum = 0
+            end = begin
+            while end < len(nums) and subarray_sum < target:
+                subarray_sum += nums[end]
+                end += 1
+            if subarray_sum >= target:
+                min_length = min(min_length, end - begin)
+        if min_length == len(nums) + 1:
+            return 0
+        return min_length
+```
+
+
+## 3rd
+
+```py
+class Solution:
+    def minSubArrayLen(self, target: int, nums: List[int]) -> int:
+        assert target > 0
+        min_length = len(nums) + 1
+        subarray_sum = 0
+        left = -1 # exclusive
+        for right in range(len(nums)):
+            subarray_sum += nums[right]
+            while subarray_sum >= target:
+                min_length = min(min_length, right - left)
+                left += 1
+                subarray_sum -= nums[left]
+        if min_length == len(nums) + 1:
+            return 0
+        return min_length
+```