제출 #1093462

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
1093462		selmahbn	Mobile (BOI12_mobile)	C++17	100 / 100	699 ms	50924 KiB

mobile

#include <bits/stdc++.h>

using namespace std;

#define ll long long
#define pdl pair<double, ll>

double sp(double x1, double y1, double x2, double y2) {
    double top = x2*x2 - x1*x1 + y2*y2 - y1*y1;
    double bottom = 2*x2 - 2*x1;
    return top/bottom;
}

int main()
{
    ll n; double l;
    cin >> n >> l;
    vector<pdl> p(n);
    ll li = -1;
    vector<double> x(n);
    vector<double> y(n);
    for (ll i = 0; i < n; i++) {
        cin >> x[i] >> y[i];
        double last;
        bool gleich = false;
        while (li >= 0) {
            double lsp, i2;
            tie(lsp, i2) = p[li];
            if (x[i] == x[i2]) {
                if (abs(y[i]) < abs(y[i2])) {
                    li--;
                    continue;
                } else {
                    gleich = true;
                    break;
                }
            }
            double csp = sp(x[i], y[i], x[i2], y[i2]);
            if (csp <= lsp) {
                li--;
            } else {
                last = csp;
                break;
            }
        }
        if (gleich) continue;
        if (li == -1) p[0] = make_pair(0, i);
        else p[li+1] = make_pair(last, i);
        li++;
    }
    double maxi = 0;
    ll last = p[0].second;
    for (ll i = 0; i <= li; i++) {
        double csp, ci;
        tie(csp, ci) = p[i];
        if (csp > l || i == li) {
            if (i == li && csp <= l) last = ci;
            double dist = sqrt((x[last]-l)*(x[last]-l)+y[last]*y[last]);
            maxi = max(maxi, dist);
            if (csp > l) break;
        }
        double dist = sqrt((x[ci]-csp)*(x[ci]-csp)+y[ci]*y[ci]);
        maxi = max(maxi, dist);
        last = ci;
    }
    cout.precision(4);
    cout << fixed << maxi;
    return 0;
}

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