Submission #1096888

#	Time	Username	Problem	Language	Result	Execution time	Memory
1096888		ocasu	Mobile (BOI12_mobile)	C++17	0 / 100	460 ms	54880 KiB

mobile

#include <bits/stdc++.h>
using namespace std;

#define int long long
#define double long double

double mid(int x1, int y1, int x2, int y2){
    return (double)(x2*x2 - x1*x1 + y2*y2 - y1*y1)/(double)(2*x2-2*x1);
}

double dist(double x1, double y1, double x2, double y2){
    return (x1-x2)*(x1-x2)+(y1-y2)*(y1-y2);
}

signed main(){
    int n,l; cin>>n>>l;
    vector<int> x(n), y(n);
    for (int i=0; i<n; i++) cin>>x[i]>>y[i];

    for (int i=0; i<n; i++) y[i]=abs(y[i]);
    vector<int> a(n,0), b(n,l);
    
    stack<int> sl;
    //cout<<'\n';
    double ans=0;
    for (int i=0; i<n; i++){
        double cur = a[i];
        while (!sl.empty()) {
            cur = max(cur, mid(x[i],y[i],x[sl.top()],y[sl.top()]));
            if (y[i] >= y[sl.top()]) break;
            sl.pop();
        }
        //cout<<i<<' '<<cur<<'\n';
        ans=max(ans, dist(x[i],y[i],cur,0));
        sl.push(i);
    }
    stack<int> sr;
    //cout<<'\n';
    for (int i=n-1; i>=0; i--){
        double cur = b[i];
        while (!sr.empty()) {
            cur = min(cur, mid(x[i],y[i],x[sr.top()],y[sr.top()]));
            if (y[i] >= y[sr.top()]) break;
            sr.pop();
        }
        //cout<<i<<' '<<cur<<'\n';
        ans=max(ans, dist(x[i],y[i],cur,0));
        sr.push(i);
    }
    cout<<sqrt(ans)<<'\n';
}

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