Java
测试点3超时
import java.io.*;
import java.util.Arrays;
public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        PrintWriter writer = new PrintWriter(System.out);
        int n = Integer.parseInt(reader.readLine());
        int[] a = new int[n];
        String[] input = reader.readLine().split(" ");
        for (int i = 0; i < n; i++) {
            a[i] = Integer.parseInt(input[i]);
        }
        Arrays.sort(a);
        for (int i = n; i > 0; i--) {
            if (a[n - i] > i) {
                writer.println(i);
                writer.flush();
                return;
            }
        }
        writer.println(0);
        writer.flush();
        reader.close();
    }
}C++
#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
const int N = 100010;
int n;
int a[N];
int main() {
    scanf("%d", &n);
    for (int i = 0; i < n; i++) scanf("%d", &a[i]);
    sort(a, a + n);
    for (int i = n; i > 0; i--) {
        if (a[n - i] > i) {
            printf("%d\n", i);
            return 0;
        }
    }
    printf("0\n");
    return 0;
}