feat: add mock for find median from data stream

Author: bujosa

src/hard/find_median_from_data_stream.rs

@@ -0,0 +1,20 @@
+#![allow(dead_code)]
+struct MedianFinder {}
+
+/**
+ * `&self` means the method takes an immutable reference.
+ * If you need a mutable reference, change it to `&mut self` instead.
+ */
+impl MedianFinder {
+    fn new() -> Self {
+        todo!()
+    }
+
+    fn add_num(&self, num: i32) {
+        todo!()
+    }
+
+    fn find_median(&self) -> f64 {
+        todo!()
+    }
+}

src/hard/mod.rs

@@ -1,3 +1,4 @@
+pub mod find_median_from_data_stream;
 pub mod largest_rectangle_in_histogram;
 pub mod median_of_two_sorted_arrays;
 pub mod merge_k_sorted_lists;