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Dinitz
Sobre
O(min(m * max_flow, n^2 m))
Grafo com capacidades 1: O(min(m sqrt(m), m * n^(2/3)))
Todo vertice tem grau de entrada ou saida 1: O(m sqrt(n))
Link original: dinitz.cpp
Código
struct dinitz {
const bool scaling = false; // com scaling -> O(nm log(MAXCAP)),
int lim; // com constante alta
struct edge {
int to, cap, rev, flow;
bool res;
edge(int to_, int cap_, int rev_, bool res_)
: to(to_), cap(cap_), rev(rev_), flow(0), res(res_) {}
};
vector<vector<edge>> g;
vector<int> lev, beg;
ll F;
dinitz(int n) : g(n), F(0) {}
void add(int a, int b, int c) {
g[a].emplace_back(b, c, g[b].size(), false);
g[b].emplace_back(a, 0, g[a].size()-1, true);
}
bool bfs(int s, int t) {
lev = vector<int>(g.size(), -1); lev[s] = 0;
beg = vector<int>(g.size(), 0);
queue<int> q; q.push(s);
while (q.size()) {
int u = q.front(); q.pop();
for (auto& i : g[u]) {
if (lev[i.to] != -1 or (i.flow == i.cap)) continue;
if (scaling and i.cap - i.flow < lim) continue;
lev[i.to] = lev[u] + 1;
q.push(i.to);
}
}
return lev[t] != -1;
}
int dfs(int v, int s, int f = INF) {
if (!f or v == s) return f;
for (int& i = beg[v]; i < g[v].size(); i++) {
auto& e = g[v][i];
if (lev[e.to] != lev[v] + 1) continue;
int foi = dfs(e.to, s, min(f, e.cap - e.flow));
if (!foi) continue;
e.flow += foi, g[e.to][e.rev].flow -= foi;
return foi;
}
return 0;
}
ll max_flow(int s, int t) {
for (lim = scaling ? (1<<30) : 1; lim; lim /= 2)
while (bfs(s, t)) while (int ff = dfs(s, t)) F += ff;
return F;
}
};
// Recupera as arestas do corte s-t
vector<pair<int, int>> get_cut(dinitz& g, int s, int t) {
g.max_flow(s, t);
vector<pair<int, int>> cut;
vector<int> vis(g.g.size(), 0), st = {s};
vis[s] = 1;
while (st.size()) {
int u = st.back(); st.pop_back();
for (auto e : g.g[u]) if (!vis[e.to] and e.flow < e.cap)
vis[e.to] = 1, st.push_back(e.to);
}
for (int i = 0; i < g.g.size(); i++) for (auto e : g.g[i])
if (vis[i] and !vis[e.to] and !e.res) cut.emplace_back(i, e.to);
return cut;
}