update

Author: OneCodeMonkey

leetcode_solved/[editing]leetcode_1248_Count_Number_of_Nice_Subarrays.cpp

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+// AC:: Runtime: 36 ms, faster than 26.88% of Java online submissions for Count Number of Nice Subarrays.
+// Memory Usage: 47 MB, less than 95.84% of Java online submissions for Count Number of Nice Subarrays.
+// same thought as prefixSum, see @ https://leetcode.com/problems/subarray-sum-equals-k/discuss/1380435/O(n2)-and-O(n)-or-Two-java-solutions-with-annotation
+// T:O(n), S:O(n)
+//
+class Solution {
+    public int numberOfSubarrays(int[] nums, int k) {
+        int ret = 0, size = nums.length;
+        int oddCountSum = 0;
+        HashMap<Integer, Integer> record = new HashMap<>();
+        record.put(0, 1);
+        for (int num : nums) {
+            if (num % 2 == 1) {
+                oddCountSum++;
+            }
+
+            if (record.get(oddCountSum - k) != null) {
+                ret += record.get(oddCountSum - k);
+            }
+
+            record.merge(oddCountSum, 1, Integer::sum);
+        }
+
+        return ret;
+    }
+}