题解 | #【模板】实数域三分#

三分模板。

#include<bits/stdc++.h>
#define int long long
#define double long double
#define x first
#define y second
using namespace std;
typedef long long LL;
typedef long long ll;
typedef pair<int, int> PII;
const int N = 3e5 + 10;
const int M = 1e3 + 10;
int mod = 1e9 + 7;
struct link {
    double k, a, b;
} a[N];
int n;
double check(double x) {
    double res = 0;
    for (int i = 1; i <= n; i++) res += fabs(a[i].k * x + a[i].a) + a[i].b;
    return res;
}

void solve() {
    cin >> n;
    double l, r;
    cin >> l >> r;
    for (int i = 1; i <= n; i++) cin >> a[i].k >> a[i].a >> a[i].b;
    while (fabs(r - l) > 1e-9) {
        double mid = (l + r) / 2;
        double midmid = (mid + r) / 2;
        if (check(mid) < check(midmid)) r = midmid;
        else l = mid;
    }
    cout << fixed << setprecision(10) << check(l) << "\n";
}

signed main() {
    ios::sync_with_stdio(false);
    cin.tie(0), cout.tie(0);
    int _;
    _ = 1;
    cin >> _;
    while (_--) {
        solve();
    }
}