https://codeforces.com/contest/1851/problem/D


#include<bits/stdc++.h>
using namespace std;
#define ll long long
int main()
{
    ll i,j,k,t,n,a[200005];

    cin>>t;
    while(t--)
    {
        cin>>n;set<ll> b;
        ll s=(1+n)*n/2;
        ll x,l=0;
        for(i=1;i<n;i++)
        {
            cin>>x;
            if(x-l<=n)
                b.insert(x-l);
            l=x;
        }
        if(b.size()==n-2+(x!=s))
            cout<<"YES"<<endl;
        else
            cout<<"NO"<<endl;
    }
    return 0;
}




#include <bits/stdc++.h>
using namespace std;

using ll = long long;

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int tests;
    cin >> tests;
    while (tests--) {
        ll n;
        cin >> n;
        --n;
        vector<ll> a(n);
        for (ll &i: a) {
            cin >> i;
        }
        vector<ll> numbers(1, a[0]);
        for (int i{1}; i < n; ++i) {
            numbers.push_back(a[i] - a[i - 1]);
        }
        ++n;
        vector<bool> occurred(1 + n, false);
        vector<ll> unexpected_numbers;
        for (auto i: numbers) {
            if (1 <= i && i <= n) {
                if (occurred[i]) {
                    unexpected_numbers.push_back(i);
                } else {
                    occurred[i] = true;
                }
            } else {
                unexpected_numbers.push_back(i);
            }
        }
        vector<ll> missing_numbers;
        for (int i{1}; i <= n; ++i) {
            if (!occurred[i]) {
                missing_numbers.push_back(i);
            }
        }
        if (missing_numbers.size() == 1u) {
            ll sum = n * (n + 1) / 2;
            if (a.back() < sum && missing_numbers[0] == sum - a.back()) {
                cout << "YES\n";
            } else {
                cout << "NO\n";
            }
            continue;
        }
        if (
            unexpected_numbers.size() == 1u
            && missing_numbers.size() == 2u
            && unexpected_numbers[0] == missing_numbers[0] + missing_numbers[1]
        ) {
            cout << "YES\n";
        } else {
            cout << "NO\n";
        }
    }
    return 0;
}