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69 changes: 69 additions & 0 deletions Graph Programs/costo minimo y flujo maximo
Original file line number Diff line number Diff line change
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Dado un grafo, halla el flujo maximo y el costo minimo entre el source s y el sink t.

#define INF (1<<30)

struct edge {
int u, v, cap, flow, cost;
int rem() { return cap - flow; }
};

const int MAX = 405;
vector<int> g[MAX];
vector<edge> e; //Lista de aristas
bitset<MAX> in_queue; //Marca los nodos que estan en cola
int pre[MAX]; //Almacena el nodo anterior para construir las rutas
int dist[MAX]; //Almacena la distancia a cada nodo
int cap[MAX];
int N; //Cantidad total de nodos
int mncost, mxflow;

void add_edge(int u, int v, int cap, int cost) {
g[u].push_back(e.size());
e.push_back({u, v, cap, 0, cost});
g[v].push_back(e.size());
e.push_back({v, u, 0, 0, -cost});
}

void flow(int s, int t) {
in_queue = mxflow = mncost = 0;
while (true) {
fill(dist, dist+N, INF); dist[s] = 0;
memset(cap, 0, sizeof(cap)); cap[s] = INF;
memset(pre, -1, sizeof(pre)); pre[s] = 0;
queue<int> q;
q.push(s);
in_queue[s] = true;

while (q.size()) {
int u = q.front(); q.pop();
in_queue[u] = false;
for (int i : g[u]) {
edge &ed = e[i];
int v = ed.v;
if (ed.rem() && dist[v] > dist[u]+ed.cost) {
dist[v] = dist[u]+ed.cost;
cap[v] = min(cap[u], ed.rem());
pre[v] = i;
if (!in_queue[v]) {
q.push(v);
in_queue[v] = true;
}
}
}
}
if (pre[t] == -1) break;
mxflow += cap[t];
mncost += cap[t] * dist[t];
for(int v = t; v != s; v = e[pre[v]].u) {
e[pre[v]].flow += cap[t];
e[pre[v]^1].flow -= cap[t];
}
}
}

void init() {
e.clear();
for(int i = 0; i <= N; i++) {
g[i].clear();
}
}