제출 #657978

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
657978		chjiao	Mobile (BOI12_mobile)	C++14	0 / 100	591 ms	15956 KiB

mobile

//Binary search the shortest length from the firehose
 
#include <bits/stdc++.h>
using namespace std;
 
#define fastio	ios_base::sync_with_stdio(false);cin.tie(0)
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
 
#define FOR(i,a,b) for(ll i=a;i<=b;i++)
#define FORB(i,a,b) for(ll i=a;i>=b;i--)
 
#define getbit(mask,i) ((mask>>(i))&1)
#define getnum(i) (1<<(i))
 
#define endl "\n"
#define sz(x) (int)size(x)
#define mp make_pair
using ll = long long;
const ll MOD1 = 1e9+7;
const ll MOD2 = 998244353;
const ll MN = 1e5;
const ll MAX = LLONG_MAX;
double FLOAT_ERR = 1e-7;
double first_true_float(double lo, double hi, function<bool(double)> f) {
	// if none of the values in the range work, return hi + 1
	lo--;
	hi++;
	while (hi-lo > FLOAT_ERR) {
		double mid =  (lo + hi) / 2.0f;
		if (f(mid)) {
			hi = mid;
		} else {
			lo = mid;
		}
	}
	return lo;
}
 
int main() {
    fastio;
	//freopen("XXX.in","r",stdin);
	// freopen("XXX.out","w",stdout);
    int N;
    double L;
    cin >> N >> L;
    vector<pair<double,double>> input(N);
    for(int i=0; i<N; i++){
        cin >> input[i].first >> input[i].second;
    }
    sort(input.begin(), input.end());
    cout << setprecision(7)<<first_true_float(1, 1.5e9, [&](double x){
        double left = 0;
        FOR(i,0,N-1){
            if(x*x < input[i].second*input[i].second){
                continue;
            }
            double diviation = sqrt(x*x - input[i].second*input[i].second);
            if(input[i].first+diviation < left) continue;
            if((input[i].first-diviation) <= left){
                left = input[i].first+diviation;
            } else {
                return false;
            }
        }
        return left >= L;

    }) << endl;
}

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