#include<bits/stdc++.h>
using namespace std;
#define int long long
typedef long long ll;
long long read()
{
    long long x;scanf("%lld",&x);return x;
}
ll quick(ll a,ll b,ll mod)
{
    ll ans=1;
    while(b)
    {
        if(b&1)
            ans=ans*a%mod;
        b=b/2;
        a=a*a%mod;
    }
    return ans;
}
ll a[200010],n,p;
map<int,int>id;//表示
vector<int>pos[200010];
int ask1()
{
    int x=(1ll*rand()*rand()+rand())%n+1;
    while(x==n)
        x=(1ll*rand()*rand()+rand())%n+1;
    int y=min(n,x+1ll);
    int q=a[y]*quick(a[x],p-2,p)%p;
    ll qq=quick(q,p-2,p);
    int len=2;
    while(x!=1)//往前跳
    {
        ll v=id[a[x]*qq%p];
        if(v==0||pos[v][0]>=x)
            break;
        len++;
        x=*(lower_bound(pos[v].begin(),pos[v].end(),x)-1);

    }
    while(y!=n)
    {
        ll v=id[a[y]*q%p];
        if(v==0||pos[v].back()<=y)
            break;
        len++;
        y=*upper_bound(pos[v].begin(),pos[v].end(),y);
    }
    return len;
}
int ask2()
{
    int x=(1ll*rand()*rand()+rand())%n+1;
    while(x==n)
        x=(1ll*rand()*rand()+rand())%n+1;
    int y=min(n,x+2ll);
    int q=a[y]*quick(a[x],p-2,p)%p;//
    int qq=quick(q,p-2,p);
    int len=2;
    while(x!=1)//往前跳
    {
        ll v=id[a[x]*qq%p];
        if(v==0||pos[v][0]>=x)
            break;
        len++;
        x=*(lower_bound(pos[v].begin(),pos[v].end(),x)-1);

    }
    while(y!=n)
    {
        ll v=id[a[y]*q%p];
        if(v==0||pos[v].back()<=y)
            break;
        len++;
        y=*upper_bound(pos[v].begin(),pos[v].end(),y);
    }
    return len;
}
void work()
{
    n=read();p=read();
    id.clear();
    int sum=0;
    for(int i=1;i<=n;i++){
        a[i]=read();
    }
    for(int i=1;i<=n;i++)
    {
        if(id[a[i]]==0)
        {
            sum++;
            id[a[i]]=sum;
            pos[sum].push_back(i);
        }
    }
    int ans=-1,now=0;
    for(int i=1;i<=1000;i++){
        int t1=ask1(),t2=ask2();
        if(t1==ans)
            now++;
        if(t2==ans)
            now++;
        if(ans!=-1&&now>=6)
            break;
        ans=max(ans,max(t1,t2));
    }
    if(ans*2<n)
        ans=-1;
    cout<<ans<<'\n';
    for(int i=1;i<=sum;i++)
        pos[i].clear();
}
signed main()
{
    srand(time(0));
    for(int t=read();t;t--)
        work();
}