Add 346_Moving_Average_from_Data_Stream.java

Design/346_Moving_Average_from_Data_Stream.java

@@ -0,0 +1,22 @@
+class MovingAverage {
+    private Queue<Integer> q;
+    private int sum;
+    private int maxSize;
+
+    public MovingAverage(int size) {
+        q = new LinkedList<>();
+        maxSize = size;
+        sum = 0;
+    }
+
+    public double next(int val) {
+        sum += val;
+        q.offer(val);
+
+        if (q.size() > maxSize) {
+            sum -= q.poll();
+        }
+
+        return (double) sum / q.size();
+    }
+}