Shifted MEX

    1#include <bits/stdc++.h>
    2using namespace std;
    3typedef long long ll;
    4const int inf = 1e9;
    5const long long INF = 1e17; //❄️
    6void solve() {
    7    int n; cin >> n;
    8    vector<int> v(n);
    9    for (int i = 0; i < n; i++) {
    10        cin >> v[i];
    11    }
    12    int ans = 0;
    13    auto mex = [&](vector<int>& a) {
    14        unordered_set<int> s;
    15        for (int i = 0; i < a.size(); i++) {
    16            s.insert(a[i]);
    17        }
    18        for (int i = 0; ; i++) {
    19            if (!s.count(i)) return i;
    20        }
    21    };
    22    sort(v.begin(), v.end());
    23    for (int i = 0; i < n; i++) {
    24        int diff = 0 - v[i];
    25        vector<int> tmp(n);
    26        for (int j = 0; j < n; j++) {
    27            tmp[j] = v[j] + diff;
    28        }
    29        ans = max(ans, mex(tmp));
    30    }
    31    cout << ans << '\n';
    32}
    33int main() {
    34    ios::sync_with_stdio(0); cin.tie(0); 
    35    int t; cin >> t;
    36    while (t--) {
    37        solve();
    38    }
    39    return 0;
    40}