From 3d72b858d383218604a043de5178fec3b2d914c8 Mon Sep 17 00:00:00 2001
From: tshimosake <102135053+tshimosake@users.noreply.github.com>
Date: Mon, 29 Apr 2024 13:20:32 +0900
Subject: [PATCH] Create subarray-sum-equals-k.md

https://github.com/tshimosake/arai60/pull/6/commits
---
 subarray-sum-equals-k.md | 68 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 68 insertions(+)
 create mode 100644 subarray-sum-equals-k.md

diff --git a/subarray-sum-equals-k.md b/subarray-sum-equals-k.md
new file mode 100644
index 0000000..7e5f8c0
--- /dev/null
+++ b/subarray-sum-equals-k.md
@@ -0,0 +1,68 @@
+自分で書いてTLEしたもの。
+
+```py
+class Solution:
+    def subarraySum(self, nums: List[int], k: int) -> int:
+        res = 0
+        for index, num in enumerate(nums):
+            sum = 0
+            j = 0
+            while index + j <= len(nums) - 1:
+                sum += nums[index + j]
+                j += 1
+                if sum == k:
+                    res += 1
+        return res
+```
+
+1回目：解答を見てなんとかアクセプト。
+
+```py
+from collections import defaultdict
+class Solution:
+    def subarraySum(self, nums: List[int], k: int) -> int:
+        res = 0
+        sum_to_counts = defaultdict(int)
+        sum_to_counts[0] = 1
+        current_sum = 0
+        for num in nums:
+            current_sum += num
+            if current_sum - k in sum_to_counts:
+                res += sum_to_counts[current_sum - k]
+            sum_to_counts[current_sum] += 1
+        return res
+```
+
+2回目：renameとif節の削除。
+
+```py
+from collections import defaultdict
+class Solution:
+    def subarraySum(self, nums: List[int], k: int) -> int:
+        res = 0
+        current_sum = 0
+        sum_count = defaultdict(int)
+        sum_count[0] = 1
+        for num in nums:
+            current_sum += num
+            res += sum_count[current_sum - k]
+            sum_count[current_sum] += 1
+        return res
+```
+
+3回目：current -> cur とrename.
+
+```py
+from collections import defaultdict
+class Solution:
+    def subarraySum(self, nums: List[int], k: int) -> int:
+        res = 0
+        cur_sum = 0
+        sum_count = defaultdict(int)
+        sum_count[0] = 1
+        for num in nums:
+            cur_sum += num
+            res += sum_count[cur_sum - k]
+            sum_count[cur_sum] += 1
+        return res
+```