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dinic.cpp
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dinic.cpp
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struct dinic
{
struct edge
{
int a, b;
ll c;
edge(int a, int b, ll c) : a(a), b(b), c(c) {}
};
int s, t;
vi level;
vector<vi> adj;
vector<edge> edges;
queue<int> q;
int m = 0;
const ll INF = 1e18;
dinic(int n, int s, int t) : s(s), t(t)
{
level.resize(n + 1);
adj.resize(n + 1);
}
void add(int a, int b, ll c)
{
edges.emplace_back(a, b, c);
edges.emplace_back(b, a, 0);
adj[a].push_back(m++);
adj[b].push_back(m++);
}
bool bfs()
{
fill(all(level), -1);
level[s] = 0;
q.push(s);
while (!q.empty())
{
int a = q.front();
q.pop();
for (int id : adj[a])
{
int b = edges[id].b;
ll c = edges[id].c;
if (c == 0 || level[b] != -1) continue;
level[b] = level[a] + 1;
q.push(b);
}
}
return level[t] != -1;
}
ll dfs(int a, ll flow)
{
if (a == t || flow == 0) return flow;
for (int id : adj[a])
{
int b = edges[id].b;
ll c = edges[id].c;
if ((level[b] <= level[a]) || c == 0) continue;
ll f = dfs(b, min(flow, c));
if (f == 0) continue;
edges[id].c -= f;
edges[id ^ 1].c += f;
return f;
}
return 0;
}
ll maxflow()
{
ll ans = 0;
while (bfs())
while (ll flow = dfs(s, INF)) ans += flow;
return ans;
}
};