Welcome to Subscribe On Youtube

Question

Formatted question description: https://leetcode.ca/all/275.html

Given an array of integers citations where citations[i] is the number of citations a researcher received for their ith paper and citations is sorted in ascending order, 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.

You must write an algorithm that runs in logarithmic time.

 

Example 1:

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, their h-index is 3.

Example 2:

Input: citations = [1,2,100]
Output: 2

 

Constraints:

  • n == citations.length
  • 1 <= n <= 105
  • 0 <= citations[i] <= 1000
  • citations is sorted in ascending order.

Algorithm

First initialize left and right to 0 and len-1, then take the middle value mid, compare citations[mid] with len-mid,

  • If the former is big, right moves before mid
  • On the contrary, right moves after mid The loop condition is left<=right, and finally returns len-left.

Code

  • 
    public class H_Index_II {
        class Solution {
            public int hIndex(int[] citations) {
                int len = citations.length, left = 0, right = len - 1;
                while (left <= right) {
                    int mid = (left + right) / 2;
                    if (citations[mid] == len - mid) {
                        return len - mid;
                    }
                    else if (citations[mid] > len - mid) { // cites > h`, try next round
                        right = mid - 1;
                    }
                    else {
                        left = mid + 1;
                    }
                }
    
                return len - left;
            }
        }
    }
    
    
    ############
    
    class Solution {
        public int hIndex(int[] citations) {
            int n = citations.length;
            int left = 0, right = n;
            while (left < right) {
                int mid = (left + right + 1) >> 1;
                if (citations[n - mid] >= mid) {
                    left = mid;
                } else {
                    right = mid - 1;
                }
            }
            return left;
        }
    }
    
  • // OJ: https://leetcode.com/problems/h-index-ii/
    // Time: O(logN)
    // Space: O(1)
    class Solution {
    public:
        int hIndex(vector<int>& A) {
            int N = A.size(), L = 0, R = N - 1;
            while (L <= R) {
                int M = (L + R) / 2;
                if (A[M] >= N - M) R = M - 1;
                else L = M + 1;
            }
            return N - L;
        }
    };
    
  • class Solution:
        def hIndex(self, citations: List[int]) -> int:
            n = len(citations)
            left, right = 0, n
            while left < right:
                mid = (left + right + 1) >> 1
                if citations[n - mid] >= mid:
                    left = mid
                else:
                    right = mid - 1
            return left
    
    ############
    
    class Solution(object):
      def hIndex(self, citations):
        """
        :type citations: List[int]
        :rtype: int
        """
        if not citations:
          return 0
        n = len(citations)
        start, end = 0, n - 1
        while start < end:
          mid = start + (end - start) / 2
          if citations[mid] >= n - mid:
            end = mid
          else:
            start = mid + 1
        return n - start if citations[start] != 0 else 0
    
    
  • func hIndex(citations []int) int {
    	n := len(citations)
    	left, right := 0, n
    	for left < right {
    		mid := (left + right + 1) >> 1
    		if citations[n-mid] >= mid {
    			left = mid
    		} else {
    			right = mid - 1
    		}
    	}
    	return left
    }
    
  • function hIndex(citations: number[]): number {
        const n = citations.length;
        let left = 0,
            right = n;
        while (left < right) {
            const mid = (left + right + 1) >> 1;
            if (citations[n - mid] >= mid) {
                left = mid;
            } else {
                right = mid - 1;
            }
        }
        return left;
    }
    
    

All Problems

All Solutions