H-Index II -- LeetCode

Given an array of citations (each citation is a non-negative integer) of a researcher, write a function to compute the researcher's h-index.

According to the definition of h-index on Wikipedia: "A scientist has index h if h of his/her N papers have at least h citations each, and the other N − h papers have no more than h citations each."

For example, given citations = [3, 0, 6, 1, 5], which means the researcher has 5 papers in total and each of them had received 3, 0, 6, 1, 5 citations respectively. Since the researcher has 3 papers with at least 3 citations each and the remaining two with no more than 3 citations each, his h-index is 3.

Note: If there are several possible values for h, the maximum one is taken as the h-index.

Follow up for H-Index: What if the citations array is sorted in ascending order? Could you optimize your algorithm?

思路：二分查找。

注意搜索的边界情况。

 

 class Solution {
 public:
     int hIndex(vector<int>& citations) {
         int left = , right = citations.size() - ;
         while (left <= right) {
             int mid = left + (right - left) / ;
             if (citations[mid] < citations.size() - mid)
                 left = mid + ;
             else if (mid > left && citations[mid - ] >= citations.size() - (mid - ))
                 right = mid - ;
             else return citations.size() - mid;
         }
         return ;
     }
 };