[Leetcode] Sort, Hash -- 274. H-Index

Given an array of citations (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."

For example, given citations = [3, 0, 6, 1, 5], which 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, his h-index is 3.

Solution:

My idea is to sort the array in descending order; find the index c[i] < i+ 1

iterate to compare the index and value

if the value < index i+1, then stop and return the index as the final answer

if value == index i, return the index i+1

else it is the length of the array

         if len(citations) == 0 or citations is None:

             return 0

         citations = sorted(citations, reverse=True)

         #print ('cita: ', citations)

         for i, c in enumerate(citations):

             if i+1 > c:

                 return i

             elif i+1 == c:

                 return i+1

         return len(citations)

time complexity: o(nlogn), space complexity o(1)

2 nd method is use hashmap

time complexity o(n), space complexity o(n)

get the array value count, when the value > len(array) L, count into the hashmap[L]

--reference

http://www.cnblogs.com/yrbbest/p/5031910.html

  if len(citations) == 0 or citations is None:

             return 0

         dicCount = {}

         for ci in citations:

             if ci > len(citations):

                 if len(citations) not in dicCount:

                     dicCount[len(citations)] = 1

                 else:

                     dicCount[len(citations)] += 1

             else:

                 if ci not in dicCount:

                     dicCount[ci] = 1

                 else:

                     dicCount[ci] += 1

         #print (' dicCount : ', dicCount)

         sum = 0

         for i in range(len(citations), -1, -1):

             if i in dicCount:

                 sum += dicCount[i]

             if sum >= i:

                 return i

巴特西

[Leetcode] Sort, Hash -- 274. H-Index

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