URAL 1447. Portkey Network

#include <cstdio>#include <cstring>#include <vector>#include <algorithm>#include <iostream>#include <string>#include <vector>#include <cstdlib>#include <map>#include <ctime>#include <cmath>#include <bitset>using namespace std;typedef long long LL;typedef unsigned long long ULL;typedef vector<int> VI;typedef vector<VI> VVI;const int maxn = 1002;const int SIZE = 511111;const double eps = 1e-10;double dis[maxn][maxn];double C[maxn][maxn], D[maxn][maxn];double t[maxn];bool vis[maxn];double tc[maxn], td[maxn];double prim(int n) {double x = 0, y = 0;int i, j, k;for (i = 1; i <= n; ++i)t[i] = dis[1][i], vis[i] = false, tc[i] = C[1][i], td[i] = D[1][i];vis[1] = true;for (i = 1; i < n; ++i) {double mi = 1e6;k = 1;for (j = 1; j <= n; ++j)if (!vis[j] && mi > t[j])mi = t[j], k = j;vis[k] = true;x += tc[k];y += td[k];for (j = 1; j <= n; ++j)if (!vis[j] && dis[k][j] < t[j])t[j] = dis[k][j], td[j] = D[k][j], tc[j] = C[k][j];}return y / x;}int u[SIZE], v[SIZE], c[SIZE], d[SIZE];int cnt;int main() {ios::sync_with_stdio(false);int i, j, n, m, a, b;scanf("%d%d", &n, &m);for (i = 0; i <= n; ++i)for (j = 0; j <= n; ++j)dis[i][j] = 1e70;double rate = 1e20, pre;for (i = 0; i < m; ++i) {scanf("%d%d%d%d", u + i, v + i, c + i, d + i);C[u[i]][v[i]] = C[v[i]][u[i]] = c[i];D[u[i]][v[i]] = D[v[i]][u[i]] = d[i];}rate = 1.0;cnt = 0;while (true) {pre = rate;++cnt;for (i = 0; i < m; ++i)dis[u[i]][v[i]] = dis[v[i]][u[i]] = d[i] - rate * c[i];rate = prim(n);if (fabs(rate - pre) < eps)break;}printf("%.10f\n", rate);return 0;}