Solutions/MAXMEX at main · kainotoa/Solutions · GitHub

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//https://www.codechef.com/problems/MAXMEX


#include <bits/stdc++.h>

using namespace std;

typedef long long int ll;

typedef vector<int> vt;
typedef vector<vector<int>> vvt;

void solve();

int main() {

    ios_base::sync_with_stdio(false);
    cin.tie(0);

    int t;
    cin >> t;
    while (t--)
        solve();
    return 0;
}

void solve()
{
    ll n;
    cin >> n;

    ll m;

    cin >> m;

    int cnt = 0;
    set<int> s;
    s.insert(m);
    int a;
    for (int i = 0; i < n; i++)
    {
        cin >> a;
        s.insert(a);
        if (a != m)
            cnt++;
    }

    int last = 1;

    for (const int& a : s)
    {
        if (a == m)
            break;
        if (a - last > 1)
        {
            cnt = -1;
            break;
        }
        last = a;
    }

    cout << cnt << "\n";
}