# bzoj 4349: 最小树形图

#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);
}

posted @ 2017-01-05 21:44  AwD!  阅读(326)  评论(0编辑  收藏  举报