2020-02-13

0551.学生出勤记录I/0551-学生出勤记录I.py

@@ -4,8 +4,4 @@ def checkRecord(self, s):
         :type s: str
         :rtype: bool
         """
-        if s.count("A") > 1 or "LLL" in s:
-            return False
-
-        return True
-
+        return s.count("A") <= 1 and "LLL" not in s

0560.和为K的子数组/0560-和为K的子数组.py

@@ -5,16 +5,19 @@ def subarraySum(self, nums, k):
         :type k: int
         :rtype: int
         """
+        # prefix[i] = sum(nums[:i])
+        # prefix[j] - prefix[i] = sum(nums[i:j])
         from collections import defaultdict
-        pre_sum = 0
-        record = defaultdict(int)
-        record[0] = 1
+
+        prefix = [0 for _ in range(len(nums) + 1)]
+
+        for i, x in enumerate(nums):
+            prefix[i + 1] = prefix[i] + x
+
+        dic = defaultdict(int)
         res = 0
-        for i in range(len(nums)):
-            pre_sum += nums[i]
-
-            #ÕÒ k - pre_sum
-            res += record[pre_sum - k]
-            record[pre_sum] += 1
-
+        for i, x in enumerate(prefix):
+            res += dic[x - k]
+            dic[x] += 1
+
         return res