[LeetCode] Problem 275 - H-Index II

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Given an array of citations sorted in ascending order (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 = [0,1,3,5,6]

Output: 3

Explanation: [0,1,3,5,6] means the researcher has 5 papers in total and each of them had received 0, 1, 3, 5, 6 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.

Follow up

  1. This is a follow up problem to H-Index, where citations is now guaranteed to be sorted in ascending order.
  2. Could you solve it in logarithmic time complexity?

Code

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public int hIndex(int[] citations) {
    int n = citations.length;
    int left = 0;
    int right = n;

    while (left < right) {
        int mid = left + (right - left) / 2;

        if (citations[n - mid - 1] <= mid)
            right = mid;
        else
            left = mid + 1;
    }

    return left;
}