274. H-Index.cpp

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.







// Brute force
class Solution {
public:
    int hIndex(vector<int>& citations) {
        int n=citations.size();
        int h=1, res=0;
        while(h<=n){
            int cnt=0;
            for(int i=0;i<n;i++){
                if(citations[i]>=h) cnt++;
            }
            if(cnt>=h)
                res=h;

            h++;
        }
        return res;
    }
};






// Optimized , if array is sorted
class Solution {
public:

int hIndex(vector<int>& citations) {
        // citations can be in range of 1 t0 n
        int n=citations.size();
        int low=0, high=n-1;
        while(low<=high){
            int mid=low+(high-low)/2;
            if(citations[mid]==n-mid) return citations[mid];
            else if(citations[mid]>n-mid) high=mid-1;
            else low=mid+1;
        }
        return n - low;
    }
};