Number of Equal (CF)

// https://codeforces.com/edu/course/2/lesson/9/1/practice/contest/307092/problem/C

void solve(int &tc)
{
    ll n, m;
    cin >> n >> m;

    vector<ll> a(n), b(m);
    cin >> a >> b;

    ll i = 0, j = 0;
    ll ans = 0;
    while(i < a.size() and j < b.size())
    {
        ll cnt1 = 0, cnt2 = 0;
        ll x = a[i];
        while(j < b.size() and b[j] < x) {
            j++;
        }
        while(i < a.size() and a[i] == x) {
            i++;
            cnt1++;
        }
        while(j < b.size() and b[j] == x) {
            j++;
            cnt2++;
        }
        ans += cnt1 * cnt2;
    }
    cout << ans << endl;
}