Submission #424415

#	Time	Username	Problem	Language	Result	Execution time	Memory
424415		winstonyin	Mobile (BOI12_mobile)	C++11	100 / 100	963 ms	35476 KiB

mobile

#include <string>
#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <algorithm>
#include <vector>
#include <cmath>
#include <array>
#include <map>
#include <set>
#include <fstream>
#include <unordered_map>
#include <queue>
#include <iomanip>
using namespace std;
using pi = pair<int, int>;
using pd = pair<double, double>; 
#define ll long long
#define all(x) (x).begin(), (x).end()

int n_stations, l_highway;
vector<pd> locations; 
bool works(double radius) {
    double curr = 0;
    for(int i = 0; i < n_stations; i++) {
        double delta = sqrt(radius*radius - locations[i].second*locations[i].second);
        double left = locations[i].first - delta, right = locations[i].first + delta;
        if(left <= curr) {
            curr = max(curr, right);
        }
    }
    return curr >= l_highway;
}
int main() {
    ios_base::sync_with_stdio(0);
	cin.tie(0);
    cin >> n_stations >> l_highway;
    for(int i = 0; i < n_stations; i++) {
        double x,y; cin >> x >> y;
        locations.push_back({x,y});
    }
    double a = 0, b = 1.5e9;
    double ans; 
    while(b - a > 1e-3) {
        double m = (a+b)/2.0; 
        if(works(m)) {
            b = m;
            ans = m;
        }
        else {
            a = m;
        }
    }
    cout << fixed << setprecision(4) << ans;
    return 0;
}

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