Submission #470632

#	Time	Username	Problem	Language	Result	Execution time	Memory
470632		zxcvbnm	Mobile (BOI12_mobile)	C++14	50 / 100	493 ms	15948 KiB

mobile

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
struct P {
    ll x, y;
};
vector<P> a;
int n, L;
bool ok(double r) {
    double curr = 0;
    for(int i = 0; i < n; i++) {
        if (r * r < a[i].y * a[i].y) continue;
        double sol = sqrt(r * r - a[i].y * a[i].y);
        double left = max((double) 0, a[i].x - sol);
        double right = min((double) L, a[i].x + sol);
        if (left <= curr) {
            curr = max(curr, right);
        }
    }

    return curr >= L;
}
signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cin >> n >> L;
    a.resize(n);
    for(auto& i : a) {
        cin >> i.x >> i.y;
    }

    double l = 0, r = 1e9;
    double ans = r;
    for(int rep = 0; rep < 40; rep++) {
        double mid = (l + r) / 2;
        if (rep == 0) mid = 1;
        else if (r > 1) mid = sqrt((long double) l * r);

        if (ok(mid)) {
            r = mid;
            ans = mid;
        }
        else {
            l = mid;
        }
    }

    cout << fixed << setprecision(6) << ans << "\n";
}

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