H-Index

/*
 * Problem : Process an array.
 * Input   : n, then n integers.
 * Output  : The h-index.
 * Approach: Sort and scan.
 * Time    : O(n log n)
 * Space   : O(1)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
    // This method solves the task. It receives the input and returns the answer.
    static int solve(int[] a) {
        // Step 1: Sort the citation counts in ascending order.
        java.util.Arrays.sort(a);
        int n = a.length;

        // Step 2: If the paper at index i is the weakest of the top (n - i) papers, then n - i papers have at least a[i] citations.
        // The first index where a[i] >= n - i gives the answer n - i.
        for (int i = 0; i < n; i++) {
            if (a[i] >= n - i) {
                return n - i;
            }
        }
        return 0;
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int size = scanner.nextInt();
        int[] a = new int[size];
        for (int i = 0; i < size; i++) {
            a[i] = scanner.nextInt();
        }
        System.out.println(solve(a));
    }
}