feat: find-median-from-data-stream

Author: minji-go

find-median-from-data-stream/minji-go.java

@@ -0,0 +1,45 @@
+/**
+ * <a href="https://leetcode.com/problems/find-median-from-data-stream/">week13-4. find-median-from-data-stream</a>
+ * <li>Description: Implement the MedianFinder class</li>
+ * <li>Topics: Two Pointers, Design, Sorting, Heap (Priority Queue), Data Stream</li>
+ * <li>Time Complexity: O(logN), Runtime 99ms   </li>
+ * <li>Space Complexity: O(N), Memory 63.68MB   </li>
+ */
+
+class MedianFinder {
+    PriorityQueue<Integer> head;
+    PriorityQueue<Integer> tail;
+
+    public MedianFinder() {
+        head = new PriorityQueue<>(Comparator.reverseOrder());
+        tail = new PriorityQueue<>();
+    }
+
+    public void addNum(int num) {
+        if(head.isEmpty() || num <= head.peek()) {
+            head.add(num);
+        } else {
+            tail.add(num);
+        }
+
+        if (head.size() > tail.size() + 1) {
+            tail.add(head.poll());
+        } else if (head.size() < tail.size()) {
+            head.add(tail.poll());
+        }
+    }
+
+    public double findMedian() {
+        if(head.size() == tail.size()){
+            return ((double)head.peek() + tail.peek()) / 2;
+        }
+        return head.peek();
+    }
+}
+
+/**
+ * Your MedianFinder object will be instantiated and called as such:
+ * MedianFinder obj = new MedianFinder();
+ * obj.addNum(num);
+ * double param_2 = obj.findMedian();
+ */