排序 + 枚举

#include <iostream>
#include <algorithm>

using namespace std;

const int N = 1e5 + 10;

int n;
int a[N];

int main()
{
    cin >> n;
    for (int i = 0; i < n; i ++ ) cin >> a[i];

    sort(a, a + n);

    int h = 0;
    for (int i = n - 1; ~i; i -- )
        if (a[i] > h) h ++ ;        //从后往前遍历，每有一个数大于h，h就自增1

    cout << h << endl;

    return 0;
}