274. H-Index – Leetcode Solutions

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, their h-index is 3.

Example 2:

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

class Solution:
    def hIndex(self, citations: List[int]) -> int:
        # First, sort the list in descending order. This helps us easily check
        # how many papers have at least 'h' citations.
        citations.sort(reverse=True)
        
        # Initialize the h-index to 0
        h_index = 0
        
        # Iterate over the sorted citations list
        for i, citation in enumerate(citations):
            # 'i' represents the current index (0-based), and 'citation' is the
            # number of citations for that paper.
            
            # The condition for h-index is that at least 'h' papers have 'h' or
            # more citations. Here, 'i + 1' is the count of papers considered
            # (since the index starts from 0), and 'citation' is how many citations
            # the current paper has.
            
            # If the number of citations is greater than or equal to the number
            # of papers considered (i + 1), we update the h-index.
            if citation >= i + 1:
                h_index = i + 1
            else:
                # As soon as we find a paper with fewer citations than the number
                # of papers considered, we can stop the loop because the list is
                # sorted in descending order, and any further papers will also
                # have fewer citations.
                break
        
        # Return the calculated h-index
        return h_index

class Solution {
public:
    int hIndex(vector<int>& citations) {
        // First, sort the citations array in descending order.
        // This makes it easier to find how many papers have at least 'h' citations.
        sort(citations.begin(), citations.end(), greater<int>());
        
        // Initialize h-index to 0
        int h_index = 0;

        // Iterate through the sorted list of citations
        for (int i = 0; i < citations.size(); ++i) {
            // 'i' is the current index, representing the number of papers considered (0-based index).
            // citations[i] is the number of citations for the current paper.
            
            // The h-index condition: we need at least 'h' papers with 'h' or more citations.
            // Here 'i + 1' is the number of papers considered so far (because index is 0-based),
            // and citations[i] is how many citations the current paper has.
            if (citations[i] >= i + 1) {
                // If the current paper has enough citations (>= i + 1), update the h-index.
                h_index = i + 1;
            } else {
                // If the current paper has fewer citations than the number of papers considered,
                // stop the loop since further papers will have even fewer citations (due to sorting).
                break;
            }
        }

        // Return the final h-index value
        return h_index;
    }
};

/**
 * @param {number[]} citations
 * @return {number}
 */
var hIndex = function(citations) {
    // Step 1: Sort the citations array in descending order.
    // This makes it easier to count how many papers have at least 'h' citations.
    citations.sort((a, b) => b - a);
    
    // Step 2: Initialize the h-index to 0.
    let hIndex = 0;
    
    // Step 3: Loop through the sorted citations array.
    for (let i = 0; i < citations.length; i++) {
        // 'i' is the current index (0-based), representing the number of papers considered.
        // citations[i] is the number of citations for the current paper.
        
        // The condition for h-index is that at least 'h' papers have 'h' or more citations.
        // Here, 'i + 1' represents the number of papers considered so far (since the index is 0-based).
        if (citations[i] >= i + 1) {
            // If the current paper has at least 'i + 1' citations, update the h-index.
            hIndex = i + 1;
        } else {
            // If the current paper has fewer citations than the number of papers considered,
            // we stop the loop as all subsequent papers will have fewer citations.
            break;
        }
    }
    
    // Step 4: Return the calculated h-index.
    return hIndex;
};

import java.util.Arrays;

class Solution {
    public int hIndex(int[] citations) {
        // Step 1: Sort the citations array in descending order.
        // This helps us easily check how many papers have at least 'h' citations.
        Arrays.sort(citations);
        
        // Step 2: Initialize h-index to 0.
        int hIndex = 0;
        
        // Step 3: Loop through the sorted array from the end (highest citation first).
        // Since the array is sorted in ascending order, we traverse from the last element.
        for (int i = 0; i < citations.length; i++) {
            // The current paper's citations are citations[citations.length - 1 - i].
            int citation = citations[citations.length - 1 - i];
            
            // The condition for h-index: at least 'i + 1' papers have 'i + 1' or more citations.
            // Here, 'i + 1' represents the number of papers considered so far.
            if (citation >= i + 1) {
                // If the paper's citations are greater than or equal to 'i + 1', update h-index.
                hIndex = i + 1;
            } else {
                // If the current paper has fewer citations than the number of papers considered,
                // stop the loop as all remaining papers will have fewer citations.
                break;
            }
        }
        
        // Step 4: Return the calculated h-index.
        return hIndex;
    }
}