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OI-codes/LibreOJ/2071/2071.cpp

79 lines
1.5 KiB
C++

#include <iostream>
#include <algorithm>
#include <array>
#include <iomanip>
#include <limits>
#include <vector>
using std::cin;
using std::cout;
const char endl = '\n';
const int N = 2505;
const double eps = 1e-4;
int k, n;
std::array<int, N> siz;
std::array<double, N> d;
std::array<std::array<double, N>, N> f;
std::array<std::vector<int>, N> g;
std::array<std::pair<int, int>, N> a;
void dfs(int u) {
f[u][1] = d[u];
siz[u] = 1;
for (int v : g[u]) {
dfs(v);
siz[u] += siz[v];
for (int i = std::min(siz[u], k + 1); i; i--) {
for (int j = 0; j <= std::min(siz[v], i - 1); j++) {
f[u][i] = std::max(f[u][i], f[u][i - j] + f[v][j]);
}
}
}
}
bool check(double mid) {
for (int i = 1; i <= n; i++) {
d[i] = static_cast<double>(a[i].second) - mid * a[i].first;
}
std::for_each(f.begin(), f.end(), [&](auto &x) {
std::fill(x.begin(), x.end(), std::numeric_limits<int>::min());
});
dfs(0);
return f[0][k + 1] >= 0;
}
int main() {
std::ios::sync_with_stdio(false);
cin.tie(nullptr);
cin >> k >> n;
for (int i = 1, r; i <= n; i++) {
cin >> a[i].first >> a[i].second >> r;
g[r].emplace_back(i);
}
double l = 0,
r = 10000;
while (r - l > eps) {
double mid = (l + r) / 2;
if (check(mid)) l = mid;
else r = mid;
}
cout << std::fixed << std::setprecision(3) << l << endl;
return 0;
}