import java.util.Arrays;

class Solution {
    public int solution(int[] citations) {
        int answer = 0;

        Arrays.sort(citations);
        
        for (int i = 0; i < citations.length; i++) {
            int h = citations.length - i; // from last
            
            if (citations[i] >= h) {
                answer = h;
                break;
            }
        }
   
        return answer;
    }
}
/**
[Question]
- 논문 n편 (1 <= n <= 1000)
    -> h번 이상 인용된 논문 = h편 이상 : h <= n (0 <= h <= 10000)
    -> 나머지 논문(h번 이하 인용) : n - h
    -> H-Index : h의 최댓값
- citations : 논문의 인용 횟수
- return H-Index

import java.util.Arrays;

class Solution {
    public int solution(int[] citations) {
        int answer = 0;
        
        Arrays.sort(citations);
        int len = citations.length;
        int h = 0;
        int low = 0;
        int high = len - 1;
        
        while (low <= high) {
            int mid = (low + high) / 2;
            h = len - mid;
            
            if (citations[mid] >= h) {
                if (mid == 0) {
                    answer = h;
                    break;
                }
                
                if (mid != 0 && citations[mid - 1] <= h) {
                    answer = h;      // update
                    high = mid - 1;  // move to the left
                }
                else high = mid - 1;  // move to the left
            }
            else low = mid + 1; // move to the right
        } 
        
        return answer;
    }
}