Submission #768938

#	Time	Username	Problem	Language	Result	Execution time	Memory
768938		orcslop	Mobile (BOI12_mobile)	C++17	100 / 100	672 ms	35324 KiB

mobile

#include <bits/stdc++.h>
using namespace std;
#define sz(x) (int)(x).size() 

const int MAXN = 1e6; 

int n; 
double l; 
pair<double, double> v[MAXN]; 

bool check(double rad){
    vector<pair<double, double>> intervals; 
    double curr = 0; 
    for(int i = 0; i < n; i++){
        double dist = 0; 
        if(0 <= v[i].first && v[i].first <= l){
            dist = v[i].second; 
        }
        else if(v[i].first < 0){
            dist = sqrt(v[i].first * v[i].first + v[i].second + v[i].second); 
        }
        else {
            dist=sqrt((v[i].first-l) * (v[i].first - l) + v[i].second * v[i].second); 
        }
        if(dist < rad){
            pair<double, double> range; 
            range.first = v[i].first - sqrt(rad * rad - v[i].second * v[i].second);
            range.second = v[i].first + sqrt(rad * rad - v[i].second * v[i].second); 
            if(range.first <= curr) curr = max(curr, range.second); 
            // else return false; 
        }
    }
    return curr >= l; 
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL); cout.tie(NULL);
    cin >> n >> l; 
    for(int i = 0; i < n; i++){
        cin >> v[i].first >> v[i].second; 
    }
    // cout << check(5.55); 
    double low = 0, high = (double) 2e9; 
    while (low + 0.00001 < high) {
        double mid = low + (high - low) / 2;
        if (check(mid)) high = mid;
        else low = mid;
    }
    cout << setprecision(15) << low << '\n'; 
    return 0; 
}

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