#include <bits/stdc++.h>
#define ll long long
#define ull unsigned long long
#define uint unsigned int
#define ldb long double
#define pii pair<int,int>
#define mkp make_pair
#define fr first
#define se second
#define uset unordered_set
#define umap unordered_map
#define pqueue priority_queue
#define all(_box) _box.begin(),_box.end()
#define popcount __builtin_popcount
#define ctz __builtin_ctz
#define clz __builtin_clz
#define lbd lower_bound
#define ubd upper_bound
#define deb(x) cerr<<#x<<'='<<(x)<<' '
using namespace std;
const double eps = 1e-9;
const int N = 3004;
int n, m;
vector<pair<int, double>>g[N];
double dis[N];
bool vis[N];
bool spfa(int u, double x) {
vis[u] = 1;
for (auto i : g[u]) {
int v = i.fr;
if (dis[v] > dis[u] + i.se - x) {
dis[v] = dis[u] + i.se - x;
if (vis[v] || spfa(v, x))
return 1;
}
}
vis[u] = 0;
return 0;
}
bool check(double x) {
memset(dis, 0, sizeof(dis));
memset(vis, 0, sizeof(vis));
for (int i = 1; i <= n; i++)
if (spfa(i, x))
return 1;
return 0;
}
int main() {
ios::sync_with_stdio(0);
cin.tie(0), cout.tie(0);
double l = 1e7, r = -1e7, mid;
cin >> n >> m;
for (int i = 1; i <= m; i++) {
int u, v;
double w;
cin >> u >> v >> w;
l = min(l, w), r = max(r, w);
g[u].push_back({v, w});
}
while (r - l > eps) {
mid = (l + r) / 2;
if (check(mid))
r = mid;
else
l = mid;
}
printf("%.8lf", l);
}
一本通1506:最小圈
最新推荐文章于 2024-05-01 10:47:26 发布