Create 1248_count_number_of_nice_sub_arrays.cpp (qiyuangong#31)

* Create 1248_count_number_of_nice_sub_arrays.cpp, @bhanu1131

Author: bhanu1131

cpp/1248_count_number_of_nice_sub_arrays.cpp

@@ -0,0 +1,42 @@
+class Solution {
+public:
+    int numberOfSubarrays(vector<int>& nums, int k) {
+        return atMostK(nums, k) - atMostK(nums, k - 1);
+    }
+
+private:
+    int atMostK(const vector<int>& nums, int k) {
+        int result = 0, left = 0, count = 0;
+        for (int right = 0; right < nums.size(); ++right) {
+            count += nums[right] % 2;
+            while (count > k) {
+                count -= nums[left] % 2;
+                ++left;
+            }
+            result += right - left + 1;
+        }
+        return result;
+    }
+};
+
+// Time:  O(n)
+// Space: O(k)
+class Solution2 {
+public:
+    int numberOfSubarrays(vector<int>& nums, int k) {
+        int result = 0;
+        deque<int> dq = {-1};
+        for (int i = 0; i < nums.size(); ++i) {
+            if (nums[i] % 2) {
+                dq.emplace_back(i);
+            }
+            if (dq.size() > k + 1) {
+                dq.pop_front();
+            }
+            if (dq.size() == k + 1) {
+                result += dq[1] - dq[0];
+            }
+        }
+        return result;
+    }
+};