275. H-Index II

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:

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

# @lc code=start
using LeetCode

function h_index_ii(citations::Vector{Int})
    l, r = 1, length(citations) + 1
    while l < r
        mid = l + r >> 1
        if citations[end + 1 - mid] >= mid
            l = mid
        else
            r = mid - 1
        end
    end
    return r
end
# @lc code=end

h_index_ii (generic function with 1 method)

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