H-Index II

Description

Given an array of integers citations where citations[i] is the number of citations a researcher received for their ith paper and citations is sorted in ascending order, return the researcher’s h-index.

According to the definition of h-index on Wikipedia: The h-index is defined as the maximum value of h such that the given researcher has published at least h papers that have each been cited at least h times.

You must write an algorithm that runs in logarithmic time.

Example 1:

Input: citations = [0,1,3,5,6] Output: 3 Explanation: [0,1,3,5,6] means the researcher has 5 papers in total and each of them had received 0, 1, 3, 5, 6 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, their h-index is 3.

Example 2:

Input: citations = [1,2,100] Output: 2

Constraints:

• n == citations.length
• 1 <= n <= 105
• 0 <= citations[i] <= 1000
• citations is sorted in ascending order.

Code

用 binary search 加速 H-Index 而已。

class Solution {
public:
    int hIndex(vector<int>& citations) {
        int n = citations.size();
        int l = 0, r = citations.size() - 1;
 
        while(l < r) {
            int mid = (l + r) / 2;
            if(citations[mid] >= (n - mid)) {
                r = mid;
            } else {
                l = mid + 1;
            }
        }
 
        return citations[l] >= n - l ? n - l : 0;
    }
};
 

Source

• H-Index II - LeetCode