Approach: Sort descending

def hIndex(citations):
    citations.sort(reverse=True)
    h = 0
    for i, c in enumerate(citations):
        if c >= i + 1:
            h = i + 1
        else:
            break
    return h

Complexity: O(n log n) time, O(1) space.

Full Solution — all languages

class Solution:
    def hIndex(self, nums):
        nums.sort(reverse=True)
        h = 0
        for i, c in enumerate(nums):
            if c >= i + 1:
                h = i + 1
            else:
                break
        return h

import java.util.*;
class Solution {
    public int hIndex(int[] nums) {
        Arrays.sort(nums);
        int n = nums.length, h = 0;
        for (int i = 0; i < n; i++) {
            int c = nums[n - 1 - i];
            if (c >= i + 1) h = i + 1;
            else break;
        }
        return h;
    }
}

#include <bits/stdc++.h> using namespace std;
class Solution {
    public: int hIndex(vector<int>& nums) {
        sort(nums.begin(), nums.end());
        int n = (int)nums.size(), h = 0;
        for (int i = 0; i < n; i++) {
            int c = nums[n - 1 - i];
            if (c >= i + 1) h = i + 1;
            else break;
        }
        return h;
    }
};

/**
 * @param {number[]} nums
 * @return {number}
 */ var hIndex = function(nums) {
    nums.sort((a, b) => b - a);
    let h = 0;
    for (let i = 0; i < nums.length; i++) {
        if (nums[i] >= i + 1) h = i + 1;
        else break;
    }
    return h;
};

H-Index

Example 1

Example 2

Constraints