274

274. H-Index (Medium)

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."

Example:

Input: citations = [3,0,6,1,5]
Output: 3 
Explanation: [3,0,6,1,5] 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, her h-index is 3.

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

Related Topics:
Hash Table, Sort

Similar Questions:

• H-Index II (Medium)

Solution 1.

// OJ: https://leetcode.com/problems/h-index/
// Author: github.com/lzl124631x
// Time: O(NlogN)
// Space: O(1)
class Solution {
public:
    int hIndex(vector<int>& A) {
        sort(begin(A), end(A));
        int L = 0, R = A.size() - 1, N = A.size();
        while (L <= R) {
            int M = (L + R) / 2;
            if (A[M] < N - M) L = M + 1;
            else R = M - 1;
        }
        return N - L;
    }
};

Solution 2.

// OJ: https://leetcode.com/problems/h-index/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(N)
class Solution {
public:
    int hIndex(vector<int>& A) {
        int N = A.size(), sum = 0;
        vector<int> cnt(N + 1);
        for (int n : A) cnt[min(n, N)]++;
        for (int i = N; i >= 0; --i) {
            sum += cnt[i];
            if (sum >= i) return i;
        }
        return -1;
    }
};