274 H-Index

Given an array of integers citations where citations[i] is the number of citations a researcher received for their i-th paper, compute the researcher's h-index.

The h-index is defined as: A scientist has index h if h of their 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: The researcher has 5 papers in total.
3 of them have at least 3 citations each and the remaining 2 have no more than 3 citations each.

Example 2:

Input: citations = [1,3,1]
Output: 1

Constraints:

• n == citations.length
• 1 <= n <= 5000
• 0 <= citations[i] <= 1000

Approach (Sorting / Greedy)

1. Sort citations.
2. Iterate through the sorted array from large to small number. For each paper at index i, check if citation is large or equal to count.

Time Complexity: O(n log n)
Space Complexity: O(1) if in-place sorting.

Solution:

Java Solution

class Solution {
    public int hIndex(int[] citations) {
        Arrays.sort(citations);
        var h = 0;
        for(var i = citations.length - 1; i >= 0; i--) {
            if(citations[i] >= citations.length - i) {
                h = citations.length - i;
            } else {
                break;
            }
        }
        return h;
    }
}

Kotlin Solution

class Solution {
    fun hIndex(citations: IntArray): Int {
        citations.sortDescending()
        var h = 0
        for(i in citations.indices) {
            if(citations[i] >= i + 1) {
                h = i + 1
            } else {
                break
            }
        }
        return h
    }
}

Golang Solution

func hIndex(citations []int) int {
    sort.Sort(sort.Reverse(sort.IntSlice(citations)))
    h := 0
    for i := 0; i< len(citations); i++ {
        if citations[i] >= i + 1 {
            h = i + 1
        } else {
            break
        }
    }
    return h
}