Create 275. H-Index II.md

solutions/275. H-Index II.md

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+# [275. H-Index II](https://leetcode.com/problems/h-index-ii/)
+# 思路
+这题实际上是[274. H-Index](https://leetcode.com/problems/h-index/)的简化版，274题引用列表没有排好序此题已经排序了。
+所以会做274题的话此题肯定没问题，[274题思路二](https://github.com/ShusenTang/LeetCode/blob/master/solutions/274.%20H-Index.md)其实就和此题的解法类似，复杂度为O(logn)，这里不再赘述。
+
+# C++
+``` C++
+class Solution {
+public:
+    int hIndex(vector<int>& citations) {
+        int n = citations.size();
+        if(!n) return 0;
+        int left = 0, right = n - 1;
+        while(left < right){
+            int mid = (left + right) >> 1;
+            if(n - mid == citations[mid]) return citations[mid];
+            if(n - mid > citations[mid]) left = mid + 1;
+            else right = mid;
+        }
+        return min(citations[left], n - left); // left == right
+    }
+};
+```