Add graph/dinic.cc

Signed-off-by: subcrip <contact@subc.rip>

graph/dinic.cc

@@ -0,0 +1,70 @@
+struct dinic {
+    struct edge {
+        int to;
+        ll cap;
+        ll flow;
+        int rev;
+    };
+
+    vector<vector<edge>> edges;
+    vector<int> layer;
+    vector<bool> vis;
+
+    dinic(int n) : edges(n + 1), layer(n + 1), vis(n + 1) {}
+
+    void add_edge(int from, int to, ll cap) {
+        edges[from].push_back({ to, cap, 0, int(edges[to].size()) });
+        edges[to].push_back({ from, 0, 0, int(edges[from].size() - 1)});
+    }
+
+    bool bfs(int s, int t) {
+        layer.assign(edges.size(), 0);
+        deque<pii> dq;
+        layer[s] = 1;
+        dq.emplace_back(s, 1);
+        while (dq.size()) {
+            popfront(dq, v, l);
+            for (auto&& e : edges[v]) {
+                if (layer[e.to] == 0 and e.cap > e.flow) {
+                    layer[e.to] = l + 1;
+                    dq.emplace_back(e.to, l + 1);
+                }
+            }
+        }
+        return layer[t] != 0;
+    }
+
+    ll dfs(int s, int t, ll cap) {
+        if (vis[s]) {
+            return 0;
+        }
+        vis[s] = 1;
+        if (s == t) {
+            return cap;
+        }
+        ll res = 0;
+        int n = edges[s].size();
+        for (int i = 0; i < n; ++i) {
+            auto e = edges[s][i];
+            if (e.cap > e.flow and layer[e.to] == layer[s] + 1) {
+                ll nw = dfs(e.to, t, min(cap - res, e.cap - e.flow));
+                edges[s][i].flow += nw;
+                edges[e.to][e.rev].flow -= nw;
+                res += nw;
+                if (res == cap) {
+                    return res;
+                }
+            }
+        }
+        return res;
+    }
+
+    ll run(int s, int t) {
+        ll res = 0;
+        while (bfs(s, t)) {
+            vis.assign(edges.size(), 0);
+            res += dfs(s, t, LLONG_MAX);
+        }
+        return res;
+    }
+};