Submission #1055461

#	Time	Username	Problem	Language	Result	Execution time	Memory
1055461		lucascgar	Mobile (BOI12_mobile)	C++17	16 / 100	1092 ms	24660 KiB

mobile

#include <bits/stdc++.h>

// #pragma GCC optimize("Ofast,unroll-loops")
// #pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")

using namespace std;

/*
chutar resposta x:
p toda torre achar achar menor e maior ponto com distância menor que x
se intervalo tem algum ponto cego: x é válido
se não, nn é

achar pontos p torre: busca binária

*/

mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count()); // overclock random

typedef pair<int,int> pii;
typedef pair<long long, long long> pll;
typedef pair<double, double> pdd;

const int MAXN = 1e6+10;
const double PRECISION = 1e-8;

long double dist(pdd a, pdd b){
    long double x = abs(a.first-b.first), y = abs(a.second-b.second);
    return x*x + y*y;
}

pii p[MAXN];
int l;
double left(int t, double d){
    if (p[t].first < 0) return 0;
    double in=0, fi = min(l,p[t].first), me;
    long double sq=d*d;
    
    if (dist({fi, 0}, p[t]) > sq) return -1;
    if (dist({0, 0}, p[t]) <= sq) return 0;

    while (fi-in>=PRECISION/10){
        
        me = (in+fi)/2.00;
        if (dist({me,0}, p[t]) <= sq){
            fi = me;
        }else in = me;
    }

    return fi;

}

double right(int t, double d){
    if (p[t].first > l) return l;

    double in=max(0, p[t].first), fi = l, me;
    long double sq = d*d;

    if (dist({in,0}, p[t]) > sq) return -1;
    if (dist({l, 0}, p[t]) <= sq) return l;

    while (fi-in>=PRECISION/10){
        me = (in+fi)/2.00;

        if (dist({me, 0}, p[t]) <= sq){
            in = me;
        }else fi = me;

    }
    return in;

}

signed main(){
    std::ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    // freopen("test.in", "r", stdin);
    // freopen("test.out", "w", stdout);
    cout << fixed << setprecision(6);

    int n;
    cin >> n >> l;

    for (int i=0;i<n;i++){
        cin >> p[i].first >> p[i].second;
    }

    double in=0, fi = 3e9, me;

    while (fi-in >= PRECISION){
        me = (in+fi)/2.00;

        set<pdd> cv;

        for (int i=0;i<n;i++){
            double lf = left(i, me), rg = right(i, me);
            if (lf != -1 && rg != -1) cv.emplace(lf, rg);
        }

        double r=0;
        bool vl = 0;
        for (const pdd &x:cv){
            if (x.first > r && x.first-r > PRECISION){
                vl=1;
                break;
            }
            r = max(r, x.second);        
        }
        if (vl) in=me;
        else fi=me;

    }

    cout << in << '\n';

    return 0;
}

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