274. H-Index

Problem

Given an array of integers citations where citations[i] is the number of citations a researcher received for their ith paper, return compute the researcher's h-index.

According to the definition of h-index on Wikipedia: A scientist has an index h if h of their n papers have at least h citations each, and the other n − h papers have no more than h citations each.

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

  Example 1:

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, their h-index is 3.

Example 2:

Input: citations = [1,3,1]
Output: 1

  Constraints:

• n == citations.length

• 1 <= n <= 5000

• 0 <= citations[i] <= 1000

Solution

class Solution {
    public int hIndex(int[] citations) {
        // Sort array then traverse from end keep track of counter denoting total elements seen so
        // far
        Arrays.sort(citations);
        int count = 0;
        int hIndex = 0;
        for (int i = citations.length - 1; i >= 0; i--) {
            if (i == citations.length - 1 && count == citations[i]) {
                hIndex = citations[i];
                return hIndex;
                //  Ex:- 7 10--> counter =8
            } else if (citations[i] <= count && count < citations[i + 1]) {
                hIndex = count;
                return hIndex;
                // Ex:- 7 9 --> counter 6 (incuding 7 there willbe 7 elements)
            } else if (citations[i] == count + 1) {
                hIndex = count + 1;
                return hIndex;
            } else {
                count++;
            }
        }
        // case when no element is hindex so far
        if (count < citations[0]) {
            hIndex = count;
        }
        return hIndex;
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).