Create moving-average-from-data-stream.cpp

C++/moving-average-from-data-stream.cpp

@@ -0,0 +1,31 @@
+// Time:  O(1)
+// Space: O(w)
+
+class MovingAverage {
+public:
+    /** Initialize your data structure here. */
+    MovingAverage(int size) : size_(size), sum_(0) {
+    }
+
+    double next(int val) {
+        if (q_.size() == size_) {
+            sum_ -= q_.front();
+            q_.pop();
+        }
+        q_.emplace(val);
+        sum_ += val;
+        return 1.0 * sum_ / q_.size();
+    }
+
+private:
+    int size_;
+    int sum_;
+    queue<int> q_;
+};
+
+/**
+ * Your MovingAverage object will be instantiated and called as such:
+ * MovingAverage obj = new MovingAverage(size);
+ * double param_1 = obj.next(val);
+ */
+