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Min Cost Arborescence.cpp
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Min Cost Arborescence.cpp
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// Min Cost Arboroscense class in C++
// Directed MST
// dir_mst returns the cost O(EV)?
struct Edge {
int u, v;
ll dist;
int kbps;
};
struct MinCostArborescence{
int n, m;
Edge allEdges[MAX];
int done[62], prev[62], id[62];
ll in[62];
void init(int n)
{
this->n = n;
m = 0;
}
void add_Edge(int u, int v, ll dist)
{
allEdges[m++] = {u,v,dist,0};
}
void add_Edge(Edge e)
{
allEdges[m++] = e;
}
ll dir_mst(int root) {
ll ans = 0;
while (true) {
for (int i = 0; i < n; i++) in[i] = INF;
for (int i = 0; i < m; i++) {
int u = allEdges[i].u;
int v = allEdges[i].v;
if (allEdges[i].dist < in[v] && u != v) {
in[v] = allEdges[i].dist;
prev[v] = u;
}
}
for (int i = 0; i < n; i++) {
if (i == root) continue;
if (in[i] == INF) return -1;
}
int cnt = 0;
memset(id, -1, sizeof(id));
memset(done, -1, sizeof(done));
in[root] = 0;
for (int i = 0; i < n; i++)
{
ans += in[i];
int v = i;
while (done[v] != i && id[v] == -1 && v != root) {
done[v] = i;
v = prev[v];
}
if (v != root && id[v] == -1) {
for (int u = prev[v]; u != v; u = prev[u])
id[u] = cnt;
id[v] = cnt++;
}
}
if (cnt == 0) break;
for (int i = 0; i < n; i++)
if (id[i] == -1) id[i] = cnt++;
for (int i = 0; i < m; i++) {
int v = allEdges[i].v;
allEdges[i].u = id[allEdges[i].u];
allEdges[i].v = id[allEdges[i].v];
if (allEdges[i].u != allEdges[i].v)
allEdges[i].dist -= in[v];
}
n = cnt;
root = id[root];
}
return ans;
}
} Arboroscense;