题解 | 相助(easy)

void mktx()
{
    int n;
    cin>>n;
    vector<int>a(n+1);
    for(int i=1;i<=n;i++) QuickRead::cin>>a[i];
    if(n==1) QuickRead::cout<<-1;
    else
    {
        if(a[1]==a[n]) QuickRead::cout<<1;
        else
        {
            if(n<=3) QuickRead::cout<<-1;
            else
            {
                for(int i=2;i<n-1;i++)
                {
                    if(a[1]==a[i]&&a[i+1]==a[n])
                    {
                        QuickRead::cout<<2;
                        return;
                    }
                }
                QuickRead::cout<<-1;
            }
        }
    }
}