Submission #445978

#	Time	Username	Problem	Language	Result	Execution time	Memory
445978		Qw3rTy	Mobile (BOI12_mobile)	C++11	100 / 100	833 ms	34736 KiB

mobile

#include <bits/stdc++.h>
#define int long long
#define db double
#define delta 1e-6
#define pi pair<int,int>
#define pb pair<db,db>
#define fi first
#define se second
using namespace std;

const int maxN = 1e6+5;

int N,L;
pi tower[maxN];
pb inter[maxN]; //intersections

bool works(db r){
	for(int i = 1; i <= N; ++i) {
		inter[i].fi = tower[i].fi - sqrt(r*r - tower[i].se*tower[i].se);
		inter[i].se = tower[i].fi + sqrt(r*r - tower[i].se*tower[i].se);
	}
	db curr = 0;
	for(int i = 1; i <= N; ++i){
		if(inter[i].fi > inter[i].se)continue;
		if(inter[i].fi <= curr)curr = max(curr,inter[i].se);
	}
	if(curr >= L)return true;
	return false;
}

signed main(){
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	//freopen("../test.in","r",stdin);
	cin >> N >> L;
	for(int i = 1; i <= N; ++i)cin >> tower[i].fi >> tower[i].se;
	db low = 1; db high = L;
	while(abs(high-low) > delta){
		db mid = (low+high)/2;
		if(works(mid))high = mid;
		else low = mid + delta;
	}
	cout << setprecision(12) << low  << '\n';
	return 0;
}

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