Saturday, June 22, 2024

# Codeforces Round #425 (Div. 2), problem: (C) Strange Radiation Solution In C/C++

```#include <bits/stdc++.h>

using namespace std;

using ll = long long;
using ld = long double;
using D = double;
using uint = unsigned int;
template<typename T>
using pair2 = pair<T, T>;

#ifdef WIN32
#define LLD "%I64d"
#else
#define LLD "%lld"
#endif

#define pb push_back
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define fi first
#define se second

const int OPEN = 1;
const int CLOSE = -1;

struct tsob
{
int x, t, id;
};

inline bool operator<(const tsob &a, const tsob &b)
{
if (a.x != b.x) return a.x < b.x;
return a.t == OPEN && b.t == CLOSE;
}

const int maxn = 100005;
const int DR = 1000000;

int curb[2];
vector<tsob> sobs;
int x[maxn], v[maxn], dir[maxn], dist[maxn];
int n, s;

bool can(ld t)
{
sobs.clear();
curb[0] = 0;
curb[1] = 0;
for (int i = 0; i < n; i++)
{
if (dist[i] <= (ll)v[i] * t)
{
curb[dir[i]]++;
} else if (dist[i] <= (ll)(v[i] + s) * t)
{
// A * r + B = 0
ld A = (ld)1 / (s - v[i]) - (ld)v[i] / (s - v[i]) / (s + v[i]);
ld B = (ld)dist[i] / (s + v[i]) - t;
ld r = -B / A;
if (dir[i] == 0)
{
sobs.pb({x[i], OPEN, dir[i]});
sobs.pb({lround(min((ld)DR + 1, floor(x[i] + r))), CLOSE, dir[i]});
} else
{
sobs.pb({lround(max((ld)-1.0, ceil(x[i] - r))), OPEN, dir[i]});
sobs.pb({x[i], CLOSE, dir[i]});
}
}
}
if (curb[0] > 0 && curb[1] > 0) return true;
sort(all(sobs));
for (auto t : sobs)
{
curb[t.id] += t.t;
if (curb[0] > 0 && curb[1] > 0) return true;
}
return false;
}

int main()
{
scanf("%d%d", &n, &s);
for (int i = 0; i < n; i++)
{
scanf("%d%d%d", &x[i], &v[i], &dir[i]);
dir[i]--;
if (dir[i] == 0) dist[i] = x[i];
else dist[i] = DR - x[i];
}
ld l = 0;
ld r = 1e6;
for (int IT = 0; IT < 50; IT++)
{
ld m = (l + r) / 2;
if (can(m)) r = m;
else l = m;
}
cout.precision(20);
cout << (double)(l + r) / 2 << endl;
return 0;
}```

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