Network Flow: Dinic

Dinic.cpp

@@ -0,0 +1,65 @@
+struct Dinic {
+    typedef int flow_t;
+
+    struct Edge {
+        int nxt;
+        flow_t res;  // residual flow
+        size_t inv;  // inversed edge index
+        Edge(int n, flow_t r, size_t v) : nxt(n), res(r), inv(v) {}
+    };
+
+    int n;
+    vector<vector<Edge>> adj;
+    vector<int> q, lvl, start;
+
+    Dinic(int _n) {
+        n = _n;
+        adj.resize(n);
+    }
+    void add_edge(int a, int b, flow_t cap, flow_t cap_inv=0) {
+        adj[a].emplace_back(b, cap, adj[b].size());
+        adj[b].emplace_back(a, cap_inv, adj[a].size() - 1);
+    }
+    bool assign_level(int src, int sink) {
+        int t = 0;
+        memset(&lvl[0], 0, sizeof(lvl[0]) * n);
+        lvl[src] = 1;
+        q[t++] = src;
+        for (int h = 0; h < t && !lvl[sink]; h++) {
+            int cur = q[h];
+            for (auto& e : graph[cur]) {
+                if (l[e.nxt] == 0 && e.res > 0) {
+                    lvl[e.nxt] = l[cur] + 1;
+                    q[t++] = e.nxt;
+                }
+            }
+        }
+        return lvl[sink] != 0;
+    }
+    flow_t block_flow(int cur, int sink, flow_t cur_flow) {
+        if (cur == sink) return cur_flow;
+        for (int& i = start[cur]; i < adj[cur].size(); i++) {
+            auto& e = adj[cur][i];
+            if (e.res > 0 && lvl[e.nxt] == lvl[cur] + 1) {
+                if (flow_t res = block_flow(e.nxt, sink, min(e.res, cur_flow))) {
+                    e.res -= res;
+                    adj[e.nxt][e.inv].res += res;
+                    return res;
+                }
+            }
+        }
+        return 0;
+    }
+    flow_t solve(int src, int sink) {
+        q.resize(n);
+        lvl.resize(n);
+        start.resize(n);
+        flow_t ans = 0;
+        while (assign_level(src, sink)) {
+            memset(&start[0], 0, sizeof(start[0]) * n);
+            while (flow_t flow = block_flow(src, sink, numeric_limits<flow_t>::max()))
+                ans += flow;
+        }
+        return ans;
+    }
+};