274. H-Index #

Problem #

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 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, her h-index is 3.

Note:

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

Problem Summary #

Find the h-index. Definition of the h-index value: if among his/her N papers, at least h papers have h citations, and the other N-h papers have no more than h citations.

Solution Approach #

You can first sort the numbers in the array in ascending order. Since we need to find the maximum h-index, start from the end of the array and search backward. Find the first array value that is less than the total length minus the index; this value is the h-index.

Code #

package leetcode

// Solution One
func hIndex(citations []int) int {
	n := len(citations)
	buckets := make([]int, n+1)
	for _, c := range citations {
		if c >= n {
			buckets[n]++
		} else {
			buckets[c]++
		}
	}
	count := 0
	for i := n; i >= 0; i-- {
		count += buckets[i]
		if count >= i {
			return i
		}
	}
	return 0
}

// Solution Two
func hIndex1(citations []int) int {
	quickSort164(citations, 0, len(citations)-1)
	hIndex := 0
	for i := len(citations) - 1; i >= 0; i-- {
		if citations[i] >= len(citations)-i {
			hIndex++
		} else {
			break
		}
	}
	return hIndex
}