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

using ll = long long;

ll qpow(ll a, ll b, ll p)
{
    ll ret = 1;
    while(b)
    {
        if(b & 1) ret = ret * a % p;
        a = a * a % p;
        b >>= 1;
    }
    return ret;
}

int Lower(const vector<int>& vec,int x)
{
    int Left=-1,Right=vec.size();
    while (Left+1<Right)
    {
        int Mid=Left+Right>>1;
        if (vec[Mid]>=x) Right=Mid;
        else Left=Mid;
    }
    return Right;
}
int Upper(const vector<int>& vec,int x)
{
    int Left=-1,Right=vec.size();
    while (Left+1<Right)
    {
        int Mid=Left+Right>>1;
        if (vec[Mid]>x) Right=Mid;
        else Left=Mid;
    }
    return Right;
}

//(i-d, i)
int check(int i, int d, ll p, vector<ll>& b, const vector<ll>& binv, unordered_map<ll,vector<int>>& pos)
{
    //printf("check(%d, %d)\n",i,d);
    ll q = b[i] * binv[i-d] % p;
    ll qinv = binv[i] * b[i-d] % p;
    int nowans = 2;
    //jump right
    int nxtpos = i+1; ll nxtval = b[i] * q % p;
    while(1)
    {
        auto it = pos.find(nxtval);
        if(it == pos.end()) break;
        auto& vec = it->second;
        // auto jt = lower_bound(vec.begin(), vec.end(), nxtpos);
        int jt=Lower(vec,nxtpos);
        if (jt==vec.size()) break;
        // if(jt == vec.end()) break;
        //printf("jump right to %d\n",*jt);
        ++nowans;
        // nxtpos = (*jt)+1;
        nxtpos=vec[jt]+1;

        nxtval = nxtval * q % p;
    }
    //jump left
    nxtpos = i-d-1; nxtval = b[i-d] * qinv % p;
    while(1)
    {
        auto it = pos.find(nxtval);
        if(it == pos.end()) break;
        auto& vec = it->second;
        // auto jt = upper_bound(vec.begin(), vec.end(), nxtpos);
        int jt=Upper(vec,nxtpos);
        // if(jt == vec.begin()) break;
        if (jt<=0) break;
        --jt; ++nowans;
        //printf("jump left to %d\n",*jt);
        // nxtpos = (*jt)-1;
        nxtpos=vec[jt]-1;
        nxtval = nxtval * qinv % p;
    }
    //printf("i=%d, d=%d, q=%d, nowans=%d\n",i,d,q,nowans);
    return nowans;
}

void solve()
{
    mt19937_64 rnd(98275314);
    int n; ll p; scanf("%d%lld",&n,&p);
    vector<ll> b(n+1), binv(n+1);
    for(int i = 1; i <= n; ++i) scanf("%lld",&b[i]), binv[i] = qpow(b[i], p-2, p);
    int ans = 2;
    if(n == 2)
    {
        printf("2\n");
        return;
    }
    //check 1,3,5,...
    if(n >= 3)
    {
        ll q = b[3] * binv[1] % p; bool flag = true;
        for(int i = 3; i <= n; i += 2)
        {
            if(b[i] * binv[i-2] % p != q)
            {
                flag = false;
                break;
            }
        }
        if(flag) ans = max(ans, (n+1)/2);
    }
    //check 2,4,6,...
    if(n % 2 == 0 && n >= 4)
    {
        ll q = b[4] * binv[2] % p; bool flag = true;
        for(int i = 4; i <= n; i += 2)
        {
            if(b[i] * binv[i-2] % p != q)
            {
                flag = false;
                break;
            }
        }
        if(flag) ans = max(ans, n/2);
    }
    unordered_map<ll,vector<int>> pos;
    for(int i = 1; i <= n; ++i) pos[b[i]].push_back(i);
    for(int t = 1; t <= 10; ++t)
    {
        int i = abs((ll)rnd()) % (n-1) + 2;
        ans = max(ans, check(i, 1, p, b, binv, pos));
    }
    for(int t = 1; t <= 10; ++t)
    {
        int i = abs((ll)rnd()) % (n-2) + 3;
        ans = max(ans, check(i, 2, p, b, binv, pos));
    }
    if(2*ans < n) printf("-1\n");
    else printf("%d\n",ans);
}

int main()
{
    int T; scanf("%d",&T);
    while(T--)
    {
        solve();
    }
    return 0;
}