Submission #735119

#	Time	Username	Problem	Language	Result	Execution time	Memory
735119		ace_in_the_hole	Mobile (BOI12_mobile)	C++17	0 / 100	280 ms	13584 KiB

mobile

#include<bits/stdc++.h>
using namespace std;

typedef long long Int;
typedef double Real;
const Real EPS = 1e-6;
bool leq(Real x, Real y) { return x-EPS <= y; }

const int N = 1e6 + 50;
int n,L, x[N];
Int y[N];

bool check(Real dis) {
	Real rightmost = 0;
	Real d_squared = dis * dis;
	for (int i = 1; i <= n; i++) {
		if (leq(dis, y[i])) continue;
		Real lef = x[i] - sqrt(d_squared - y[i]);
		Real rig = 2*x[i] - lef;
		if (leq(lef, rightmost)) {
			rightmost = max(rightmost, rig);
			if (leq(L,rightmost)) return true;
		}
	}
	return false;
}

void solve() 
{
	cin >> n >> L;
	for (int i = 1; i <= n; i++) cin >> x[i] >> y[i];
	//preprocessing
	Real max_dist = L;
	for (int i = 1; i <= n; i++) {
		y[i] *= y[i];
		int x_dis = max(x[i], L - x[i]);
		Real cur_dist = sqrt(y[i] + 1ll * x_dis * x_dis);
		// cerr << cur_dist << '\n';
		max_dist = max(max_dist, cur_dist);
	}
	const Real DEL = 1e-3;
	Real ans = 0;
	for (Real low = 0, high = max_dist + 100; high - low >= DEL; ) {
		Real mid = (low + high) / 2;
		if (check(mid)) high = mid;
		else ans = low = mid;
	}
	cout << fixed << setprecision(15) << ans;
}

int main()
{
	ios_base::sync_with_stdio(0);
	cin.tie(0); cout.tie(0);

	#define task "WF"
	if (fopen(task".inp", "r")) {
		freopen(task".inp", "r", stdin);
		freopen(task".out", "w", stdout);
	}
	solve();
}

Compilation message (stderr)

mobile.cpp: In function 'int main()':
mobile.cpp:58:10: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   58 |   freopen(task".inp", "r", stdin);
      |   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
mobile.cpp:59:10: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   59 |   freopen(task".out", "w", stdout);
      |   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

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