new_contents: class Solution(object):
      def hIndex(self, citations):
          """
          :type citations: List[int]
          :rtype: int
          """
          n = len(citations)
          if n == 0:
              return 0
          counter = {}
          for i in range(n + 1):
              counter[i] = 0
          for citation in citations:
              if citation > n:
                  citation = n
              counter[citation] += 1
          cnt = 0
          ans = 0
          for key in range(n, -1, -1):
              cnt += counter[key]
              ans = max(ans, min(cnt, key))
          return ans
subject: add h-index