0274-h-index.rb

# frozen_string_literal: true

# 274. H-Index
# https://leetcode.com/problems/h-index
# Medium

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

According to the definition of h-index on Wikipedia: The h-index is defined as the maximum value of h such that the given researcher has published at least h papers that have each been cited at least h times.

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
=end

# @param {Integer[]} citations
# @return {Integer}
def h_index(citations)
  citations.sort.reverse.each_with_index.count(&:>)
end

# **************** #
#       TEST       #
# **************** #

require "test/unit"
class Test_h_index < Test::Unit::TestCase
  def test_
    assert_equal 3, h_index([3, 0, 6, 1, 5])
    assert_equal 1, h_index([1, 3, 1])
  end
end