package array;

/**
 * Created by gouthamvidyapradhan on 12/12/2017.
 * 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.

 Solution O(n) Replace all the citations which are greater than n with n, the result will not change with this
 operation.
 Maintain a count array with count of each citations. Sum up all the counts from n -> 0 and store this in a array S.
 Value in array index Si is number of papers having citations at least i.

 The first value at index i, from right to left in array S which has i <= Si is the answer.


 */
public class HIndex {

    public static void main(String[] args) throws Exception{
        int[] A = {3, 0, 6, 1, 5};
        System.out.println(new HIndex().hIndex(A));
    }

    public int hIndex(int[] citations) {
        int n = citations.length;
        int[] count = new int[n + 1];
        int[] S = new int[n + 1];
        for(int i = 0; i < citations.length; i ++){
            if(citations[i] > n){
                citations[i] = n;
            }
        }
        for (int citation : citations) {
            count[citation]++;
        }
        S[n] = count[n];
        for(int i = n - 1; i >= 0; i --){
            S[i] = count[i] + S[i + 1];
        }
        for(int i = n; i >= 0; i--){
            if(i <= S[i]){
                return i;
            }
        }
        return 0;
    }
}