bzoj 4349: 最小树形图

最小树形图模板题……

这种(O(nm))的东西真的能考到么……

#include <bits/stdc++.h>
#define N 60
#define INF 1000000000
using namespace std;
int n, m, nn;
double ai[N], an[N], ci[2][N][N], ans;
int bc[N];
int ini[N], vis[N], inc[N], inl[N];
int dfn;
int dfs(int t)
{
    vis[t] = dfn;
    if (vis[ini[t]] == vis[t])
        return ini[t];
    else if (vis[ini[t]]) 
        return 0;
    else return dfs(ini[t]);
}
 
int main()
{
    scanf("%d", &n);
    for (int i = 0; i <= n; ++ i)
        for (int j = 0; j <= n; ++ j)
            ci[0][i][j] = INF;
    for (int i = 1; i <= n; ++ i)
        scanf("%lf%d", &ai[i], &bc[i]), an[i] = ai[i], ci[0][0][i] = ai[i];
    scanf("%d", &m);
    for (int i = 1; i <= m; ++ i)
    {
        int a, b; double c;
        scanf("%d%d%lf", &a, &b, &c);
        if (a != b) ci[0][a][b] = min(ci[0][a][b], c);
        an[b] = min(an[b], c);
    }
    for (int i = 1; i <= n; ++ i) ans += an[i] * (bc[i] - 1);
    int tmp = 0, wh = 1; nn = n;
    while (wh)
    {
        wh = 0;
        for (int i = 1; i <= nn; ++ i)
        {
            double mn = INF;
            for (int j = 0; j <= nn; ++ j)
                if (ci[tmp][j][i] < mn)
                    mn = ci[tmp][j][i], ini[i] = j;
        }
        for (int i = 0; i <= nn; ++ i) vis[i] = 0; vis[0] = -1;
        for (int i = 1; i <= nn; ++ i)
            if (!vis[i])
            {
                dfn ++;
                int x = dfs(i);
                if (x)
                {
                    int tot = 0;
                    wh = 1;
                    for (int j = 0; j <= nn; ++ j) inc[j] = 0;
                    for (int j = ini[x]; j != x; j = ini[j]) inc[j] = 1; inc[x] = 1;
                    for (int j = 0; j <= nn; ++ j) if (!inc[j]) inl[j] = tot ++; else ans += ci[tmp][ini[j]][j];
                    for (int j = 0; j <= nn; ++ j)
                        for (int k = 0; k <= nn; ++ k)
                            ci[!tmp][j][k] = INF;
                    for (int j = 0; j <= nn; ++ j)
                        for (int k = 0; k <= nn; ++ k)
                        {
                            if (!inc[j])
                            {
                                if (!inc[k])
                                    ci[!tmp][inl[j]][inl[k]] = min(ci[!tmp][inl[j]][inl[k]], ci[tmp][j][k]);
                                else
                                    ci[!tmp][inl[j]][tot] = min(ci[!tmp][inl[j]][tot], ci[tmp][j][k] - ci[tmp][ini[k]][k]);
                            }
                            else if (!inc[k])
                                    ci[!tmp][tot][inl[k]] = min(ci[!tmp][tot][inl[k]], ci[tmp][j][k]);
                        }
                    nn = tot;
                    break;
                }
            }
        if (!wh)
            for (int i = 1; i <= nn; ++ i) ans += ci[tmp][ini[i]][i];
        else tmp ^= 1;
    }
    printf("%.2lf", ans);
}