New Problem "Find Median from Data Stream"

README.md

@@ -14,6 +14,7 @@ LeetCode
 |300|[Longest Increasing Subsequence](https://leetcode.com/problems/longest-increasing-subsequence/)  | [C++](./algorithms/cpp/longestIncreasingSubsequence/longestIncreasingSubsequence.cpp)|Medium|
 |299|[Bulls and Cows](https://leetcode.com/problems/bulls-and-cows/)  | [C++](./algorithms/cpp/bullsAndCows/bullsAndCows.cpp)|Easy|
 |297|[Serialize and Deserialize Binary Tree](https://leetcode.com/problems/serialize-and-deserialize-binary-tree/)  | [C++](./algorithms/cpp/serializeAndDeserializeBinaryTree/SerializeAndDeserializeBinaryTree.cpp)|Medium|
+|295|[Find Median from Data Stream](https://leetcode.com/problems/find-median-from-data-stream/) | [C++](./algorithms/cpp/findMedianFromDataStream/FindMedianFromDataStream.cpp)|Hard|
 |292|[Nim Game](https://leetcode.com/problems/nim-game/)  | [C++](./algorithms/cpp/nimGame/nimGame.cpp)|Easy|
 |290|[Word Pattern](https://leetcode.com/problems/word-pattern/) | [C++](./algorithms/cpp/wordPattern/WordPattern.cpp)|Easy|
 |287|[Find the Duplicate Number](https://leetcode.com/problems/find-the-duplicate-number/)  | [C++](./algorithms/cpp/findTheDuplicateNumber/findTheDuplicateNumber.cpp)|Hard|

algorithms/cpp/findMedianFromDataStream/FindMedianFromDataStream.cpp

@@ -0,0 +1,76 @@
+// Source : https://leetcode.com/problems/find-median-from-data-stream/
+// Author : Hao Chen
+// Date   : 2015-11-14
+
+/*************************************************************************************** 
+ *
+ * Median is the middle value in an ordered integer list. If the size of the list is 
+ * even, there is no middle value. So the median is the mean of the two middle value.
+ * Examples: 
+ * [2,3,4] , the median is 3
+ * [2,3], the median is (2 + 3) / 2 = 2.5 
+ * 
+ * Design a data structure that supports the following two operations:
+ * 
+ * void addNum(int num) - Add a integer number from the data stream to the data 
+ * structure.
+ * double findMedian() - Return the median of all elements so far.
+ * 
+ * For example:
+ * 
+ * add(1)
+ * add(2)
+ * findMedian() -> 1.5
+ * add(3) 
+ * findMedian() -> 2
+ * 
+ * Credits:Special thanks to @Louis1992 for adding this problem and creating all test 
+ * cases.
+ *               
+ ***************************************************************************************/
+
+
+class MedianFinder {
+    
+private:
+    //we seprate the sorted array to two parts
+    multiset<int> first, second;
+    
+public:
+
+    // Adds a number into the data structure.
+    void addNum(int num) {
+        if (first.empty() || num <= *(first.rbegin()) ) {
+            first.insert(num);
+        } else {
+            second.insert(num);
+        }
+        
+        if (first.size() > second.size() + 1) {
+            auto it = first.end();
+            it--;
+            second.insert(*(it));
+            first.erase(it);
+        }
+        
+        if ( first.size() < second.size() ) {
+            first.insert(*(second.begin()));
+            second.erase(second.begin());
+        }
+    }
+
+    // Returns the median of current data stream
+    double findMedian() {
+        if (first.size()> second.size()) {
+            return *(first.rbegin());
+        }
+        double x = *first.rbegin();
+        double y = *second.begin();
+        return (x+y)/2;
+    }
+};
+
+// Your MedianFinder object will be instantiated and called as such:
+// MedianFinder mf;
+// mf.addNum(1);
+// mf.findMedian();