rt，应该是 $O(n \log V)$（$V$ 是值域），但是 T 了 $24$ 个点。

赛时提交。

#include <bits/stdc++.h>
#define _for(i, a, b)  for (int i = (a); i <= (b); i ++ )
#define ll long long
using namespace std;
const int N = 2e5 + 5, M = 1e6 + 5;
const ll inf = (ll)2e18 + 5;
int n, K, V; ll ans; priority_queue<int> q;
struct Number { int a, b; } t[N];
struct Seg_Tree {
	#define lc p << 1
	#define rc p << 1 | 1
	#define mid ((tr[p].l + tr[p].r) >> 1)
	struct Tree { int l, r; ll val; } tr[M << 2];
	inline int len(int p) { return tr[p].r - tr[p].l + 1; }
	inline void push_up(int p) { tr[p].val = tr[lc].val + tr[rc].val; }
	void build(int p, int l, int r) {
		tr[p].l = l, tr[p].r = r, tr[p].val = 0;
		if (l == r)  return ;
		build(lc, l, mid), build(rc, mid + 1, r), push_up(p);
	}
	void update(int p, int x, int k) {
		if (x < 1 || x > V)  return ;
		if (len(p) == 1) { tr[p].val += k; return ; }
		update(x <= mid ? lc : rc, x, k), push_up(p);
	}
	ll query(int p, int l, int r) {
		if (l > r)  return 0;
		if (l <= tr[p].l && tr[p].r <= r)  return tr[p].val;
		ll res = 0;
		if (l <= mid)  res += query(lc, l, r);
		if (r > mid)  res += query(rc, l, r);
		return res;
	}
} T[2];
inline void solve() {
	while (q.size())  q.pop();
	cin >> n >> K, V = 0, ans = inf; int pos, cnt;
	_for (i, 1, n)  cin >> t[i].a;
	_for (i, 1, n)  cin >> t[i].b, V = max(V, t[i].b);
	sort(t + 1, t + n + 1, [&] (Number u, Number v) { return u.a ^ v.a ? u.a < v.a : u.b < v.b; }), T[0].build(1, 1, V), T[1].build(1, 1, V);
	_for (i, 1, K - 1)  T[0].update(1, t[i].b, 1), T[1].update(1, t[i].b, t[i].b), q.push(t[i].b);
	_for (i, K, n) {
		T[0].update(1, t[i].b, 1), T[1].update(1, t[i].b, t[i].b);
		if (q.empty() || q.top() > t[i].b) {
			if (i > K)  q.pop();
			q.push(t[i].b);
		}
		pos = q.top(), cnt = T[0].query(1, 1, pos - 1), ans = min(ans, 1ll * t[i].a * (T[1].query(1, 1, pos - 1) + 1ll * pos * (K - cnt)));
	}
	cout << ans << "\n";
}
int main() {
	ios :: sync_with_stdio(false), cin.tie(0), cout.tie(0);
	int T; cin >> T;
	while (T -- )  solve();
	return 0;
}