correct the algorithm from O(n) to O(log(n))

README.md

@@ -17,7 +17,7 @@ LeetCode
 |283|[Move Zeroes](https://leetcode.com/problems/move-zeroes/)  | [C++](./algorithms/cpp/moveZeroes/moveZeroes.cpp)|Easy|
 |279|[Perfect Squares](https://leetcode.com/problems/perfect-squares/) | [C++](./algorithms/cpp/perfectSquares/PerfectSquares.cpp)|Medium|
 |278|[First Bad Version](https://leetcode.com/problems/first-bad-version/)| [C++](./algorithms/cpp/firstBadVersion/FirstBadVersion.cpp), [Java](./algorithms/java/src/firstBadVersion/firstBadVersion.java)|Easy|
-|275|[H-Index II](https://leetcode.com/problems/h-index-ii/)| [C++](./algorithms/cpp/h-Index/h-Index_II.cpp)|Medium|
+|275|[H-Index II](https://leetcode.com/problems/h-index-ii/)| [C++](./algorithms/cpp/h-Index/h-Index.II.cpp)|Medium|
 |274|[H-Index](https://leetcode.com/problems/h-index/)| [C++](./algorithms/cpp/h-Index/h-Index.cpp)|Medium|
 |273|[Integer to English Words](https://leetcode.com/problems/integer-to-english-words/)| [C++](./algorithms/cpp/integerToEnglishWords/IntegerToEnglishWords.cpp)|Medium|
 |268|[Missing Number](https://leetcode.com/problems/missing-number/)| [C++](./algorithms/cpp/missingNumber/MissingNumber.cpp)|Medium|

algorithms/cpp/h-Index/h-Index.II.cpp

@@ -0,0 +1,33 @@
+// Source : https://leetcode.com/problems/h-index-ii/
+// Author : Hao Chen
+// Date   : 2015-11-08
+
+/*************************************************************************************** 
+ *
+ * Follow up for H-Index: What if the citations array is sorted in ascending order?
+ * Could you optimize your algorithm?
+ *               
+ ***************************************************************************************/
+
+
+
+class Solution {
+public:
+    // binary search - O(log(n))
+    int hIndex(vector<int>& citations) {
+        int n = citations.size();
+        int low = 0, high = n-1;
+
+        while( low <= high ) {
+            int mid = low + (high-low)/2;
+            if (citations[mid] == n - mid) {
+                return n - mid;
+            }else if (citations[mid] > n-mid){
+                high = mid - 1;
+            }else {
+                low = mid + 1;
+            }
+        }
+        return n-low;
+    }
+};