H-Index I, II

I. 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.

Runtime: 4ms.

class Solution {
public:
int hIndex(vector<int>& citations) {
int n = citations.size();
if(n == 0) return 0;

int i = 1;
sort(citations.begin(), citations.end());
while(i <= n){
while(citations[n - i] >= i)
i++;
return i - 1;
}
return citations[0];
}
};

II. Follow up for H-Index: What if the

citations

array is sorted in ascending order? Could you optimize your algorithm?

Runtime: 12ms.

class Solution {
public:
int hIndex(vector<int>& citations) {
int n = citations.size();
if(n == 0) return 0;

int low = 0, high = n - 1;
while(low <= high){
int mid = (low + high) / 2;

if(n - mid <= citations[mid])
high = mid - 1;
else
low = mid + 1;
}
return n - low;
}
};