Question

Formatted question description: https://leetcode.ca/all/274.html

 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."

 Example:

 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, her h-index is 3.

 Note: If there are several possible values for h, the maximum one is taken as the h-index.

Algorithm

  1. Sort all SCI papers published by him in descending order of the number of citations;
  2. Search the sorted list from front to back until the serial number of a paper is greater than the number of times the paper has been cited.

The obtained serial number minus one is the H index

Code

Java

  • 
    public class H_Index {
        class Solution {
            public int hIndex(int[] citations) {
    
                if (citations == null || citations.length == 0) {
                    return 0;
                }
    
                // @note
                Arrays.sort(citations); // 6,5,3,1,0
                for (int i = 0; i < citations.length / 2; ++i) {
                    int temp = citations[i];
                    citations[i] = citations[citations.length - i - 1];
                    citations[citations.length - i - 1] = temp;
                }
    
                for (int i = 0; i < citations.length; ++i) {
                    if (citations[i] <= i) { // @note: <i then return i+1 will not work
                        return i;
                    }
                }
    
                return citations.length;
    
            }
        }
    }
    
    
  • // OJ: https://leetcode.com/problems/h-index/
    // Time: O(NlogN)
    // Space: O(1)
    class Solution {
    public:
        int hIndex(vector<int>& A) {
            sort(begin(A), end(A));
            int L = 0, R = A.size() - 1, N = A.size();
            while (L <= R) {
                int M = (L + R) / 2;
                if (A[M] < N - M) L = M + 1;
                else R = M - 1;
            }
            return N - L;
        }
    };
    
  • class Solution(object):
      def hIndex(self, citations):
        """
        :type citations: List[int]
        :rtype: int
        """
        n = len(citations)
        dp = [0] * (n + 1)
        for c in citations:
          if c > n:
            dp[n] += 1
          else:
            dp[c] += 1
    
        total = 0
        for i in reversed(range(1, len(dp))):
          total += dp[i]
          if total >= i:
            return i
        return 0
    
    

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