题解 | #圆覆盖#

二分答案

#include <iostream>
#include <queue>
#include <map>
#include <set>
#include <cmath>
#include <cstring>
#include <algorithm>
#include <iomanip>
#include <stack>
#include <numeric>
#include <ctime>
#include <string>
#include <bitset>
#include <unordered_map>
#include <unordered_set>

using namespace std;
using ll = long long;

const ll N = 1e5+5,mod=1e9+7,inf=0x3f3f3f3f; 
const double esp=1e-6;
ll n, k;

struct Node{
    ll x, y, v;
    double R;
    bool operator<(const Node& u) const {
        return R < u.R;
    }
} a[N];

double summ[N];

bool check(double mid) {
    int len = upper_bound(a + 1, a + n + 1, Node{0, 0, 0, mid}) - a;
    return summ[len - 1] >= k;
}

void solve() {
    cin >> n >> k;
    ll sum = 0;
    for (int i = 1; i <= n; i++) {
        cin >> a[i].x >> a[i].y >> a[i].v;
        a[i].R = sqrt(a[i].x * a[i].x + a[i].y * a[i].y);
        sum += a[i].v;
    }

    if (sum < k) {
        cout << -1;
        return;
    }

    sort(a + 1, a + n + 1);
    
    for (int i = 1; i <= n; i++) {
        summ[i] = summ[i - 1] + a[i].v;
    }

    double l = 0, r = 2e9;
    
    while (fabs(r - l) > esp) {
        double mid = (r + l) / 2;
        if (check(mid)) {
            r = mid;
        } else {
            l = mid;
        }
    }

    cout << fixed << setprecision(10) << l;
}

int main() {
    ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);

    int t = 1;
    //cin >> t;

    while (t--) {
        solve();
    }

    return 0;
}