1830B - The BOSS Can Count Pairs - CodeForces Solution

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

const int SQRT = 640;
const int maxN = 200'005;
int arr[maxN];
int brr[maxN];
int cnt[2 * maxN];

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);

    int t;
    cin >> t;
    while (t--) {
        int n;
        cin >> n;

        for (int i = 0; i < n; i++) cin >> arr[i];
        for (int i = 0; i < n; i++) cin >> brr[i];

        ll ans = 0;
        for (int x = 1; x <= SQRT; x++) {
            for (int i = 1; i <= 2 * n; i++) cnt[i] = 0;
            for (int i = n - 1; i >= 0; i--) {
                if (arr[i] == x) {
                    ans += cnt[brr[i]];
                }
                ll v = (ll)x * arr[i] - brr[i];
                if (v > 0 && v <= 2*n) cnt[v]++;
            }
        }
        for (int x = 1; x <= SQRT; x++) {
            for (int i = 1; i <= 2 * n; i++) cnt[i] = 0;
            for (int j = 0; j < n; j++) {
                if (arr[j] == x) {
                    ans += cnt[brr[j]];
                }
                if (arr[j] > SQRT) {
                    ll v = (ll)x * arr[j] - brr[j];
                    if (v > 0 && v <= 2*n) cnt[v]++;
                }
            }
        }
        cout << ans << endl;
    }

    return 0;
}