I found an interesting problem on https://www.codechef.com/problems/CHFPARTY:
Tonight, Chef would like to hold a party for his $N$ friends.
All friends are invited and they arrive at the party one by one in an arbitrary order. However, they have certain conditions — for each valid $i$, when the $i$-th friend arrives at the party and sees that at that point, strictly less than $A_i$ other people (excluding Chef) have joined the party, this friend leaves the party; otherwise, this friend joins the party.
Help Chef estimate how successful the party can be — find the maximum number of his friends who could join the party (for an optimal choice of the order of arrivals).

-----Input-----
- The first line of the input contains a single integer $T$ denoting the number of test cases. The description of $T$ test cases follows.
- The first line of each test case contains a single integer $N$.
- The second line contains $N$ space-separated integers $A_1, A_2, \ldots, A_N$.

-----Output-----
For each test case, print a single line containing one integer — the maximum number of Chef's friends who could join the party.

-----Constraints-----
- $1 \le T \le 1,000$
- $1 \le N \le 10^5$
- the sum of $N$ over all test cases does not exceed $10^6$

-----Example Input-----
3
2
0 0
6
3 1 0 0 5 5
3
1 2 3

-----Example Output-----
2
4
0

-----Explanation-----
Example case 1: Chef has two friends. Both of them do not require anyone else to be at the party before they join, so they will both definitely join the party.
Example case 2: At the beginning, friends $3$ and $4$ can arrive and join the party, since they do not require anyone else to be at the party before they join. After that, friend $2$ can arrive; this friend would see that there are two people at the party and therefore also join. Then, friend $1$ will also join, so in the end, there would be $4$ people attending the party.
Example case 3: No one will attend the party because each of Chef's friends will find zero people at the party and leave, regardless of the order in which they arrive.

I tried it in Python, but could not do it. Can you solve it?
# cook your dish here
t=0
try:
 t=int(input())
except:
 pass

for _ in range(t):
 n = int(input())
 a = list(map(int, input().split()))
 
 a = sorted(a)
 
 already_present = 0
 
 for requirement in a:
  
  if already_present>=requirement:
   already_present+=1
 
 print(already_present)