Submission #932363

#	Time	Username	Problem	Language	Result	Execution time	Memory
932363		HuyAT	Mobile (BOI12_mobile)	C++14	0 / 100	1063 ms	82192 KiB

mobile

#include<bits/stdc++.h>

const int MaxN = 1e6 + 10;
const long double Eps = 1e-6;
const long double MaxV = 1e18;

int n;
long double length,x[MaxN + 1],y[MaxN + 1];

void readData(){
    std::cin >> n >> length;
    for(int i = 1;i <= n;++i){
        std::cin >> x[i] >> y[i];
    }
}
bool f(long double mid){
//    bool found = false;
    long double l = 1e10,r = 1e10;
    std::vector<std::pair<long double,long double>> v;
    for(int i = 1;i <= n;++i){
        if(mid < y[i]){
            continue;
        }
        long double distance = sqrt(mid * mid - y[i] * y[i]);
        v.emplace_back(x[i] - distance,x[i] + distance);
    }
    std::sort(v.begin(),v.end());
    if(v.empty()){
        return false;
    }
    l = v[0].first;
    r = v[0].second;
//    long double l = 1e10,r = 1e10;
    for(int i = 1;i < (int)v.size();++i){
        if(v[i].first > r && fabs(v[i].first - r) > Eps){
            return false;
        }
        r = std::max(r,v[i].second);
    }
    return ((l <= 1 || fabs(l - 1) < Eps) && (r >= length || fabs(r - length) < Eps));
}
long double solve(long double lo,long double hi){
    while(hi - lo > Eps){
        long double mid = (lo + hi) / 2;
        if(f(mid)){
            hi = mid;
        }else{
            lo = mid;
        }
//        std::cerr << mid << "\n";
    }
    return hi;
}
int main(){
    std::ios_base::sync_with_stdio(false);
    std::cin.tie(nullptr);std::cout.tie(nullptr);
    readData();
    std::cout << std::fixed << std::setprecision(6) << solve(0,MaxV * 2);
    return 0;
}

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