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cp-templates/graph/edmonds-karp.cc

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1.6 KiB
C++

struct edmonds_karp {
struct edge {
int to;
ll cap;
ll flow;
pair<int, int> rev;
int mark;
};
vector<vector<edge>> edges;
edmonds_karp(int n) : edges(n + 1) {}
void add_edge(int from, int to, ll cap, int mark = 0) {
edges[from].push_back({to, cap, 0, make_pair(to, int(edges[to].size())), mark});
edges[to].push_back({from, 0, 0, make_pair(from, int(edges[from].size() - 1)), mark});
}
ll run(int s, int t) {
int n = edges.size();
vector<pii> pa_(n + 1);
ll res = 0;
while (1) {
vector<ll> pf(n + 1);
deque<int> dq;
dq.emplace_back(s);
pf[s] = LLONG_MAX;
while (dq.size()) {
int v = dq.front(); dq.pop_front();
for (auto&& [i, ne] : enumerate(edges[v])) {
if (pf[ne.to] == 0 and ne.cap > ne.flow) {
pf[ne.to] = min(pf[v], ne.cap - ne.flow);
pa_[ne.to] = {v, i};
dq.emplace_back(ne.to);
}
}
if (pf[t] != 0) {
break;
}
}
if (pf[t] == 0) {
break;
}
int p = t;
while (pa_[p].first != 0) {
auto [x, y] = pa_[p];
edges[x][y].flow += pf[t];
auto [z, w] = edges[x][y].rev;
edges[z][w].flow -= pf[t];
p = x;
}
res += pf[t];
}
return res;
}
};