Create 最小费用最大流-Spfa

4.树和图/最小费用最大流-Spfa

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+add_edge(u, v, w, c) 连一条u到v的单向边，容量为w，花费为c，并且增加反向边
+doit(S, T, &flow, &cost), 以S为源点，T为汇点的最小费用最大流，flow为最大流量，cost为最小费用
+init() 清空边
+namespace MCMF {  
+    int cnt, head[MAXN];  
+    int dis[MAXN], vis[MAXN], pre[MAXN];  
+    struct Edge {  
+        int u, to, w, c, next;  
+    }edge[MAXN<<1];     
+    void init() {  
+        cnt = 0;  
+        memset(head, -1, sizeof head);  
+    }  
+    void add(int u, int v, int w, int c) {  
+        edge[cnt].u = u;  
+        edge[cnt].to = v;  
+        edge[cnt].w = w;  
+        edge[cnt].c = c;  
+        edge[cnt].next = head[u];  
+        head[u] = cnt++;  
+    }  
+    void add_edge(int u, int v, int w, int c) {  
+        add(u, v, w, c); add(v, u, 0, -c);  
+    }  
+    bool spfa(int S, int T) {  
+        memset(dis, 0x3f, sizeof dis);  
+        memset(vis, 0, sizeof vis);  
+        memset(pre, -1, sizeof pre);  
+        queue<int> q;  
+        q.push(S); vis[S] = 1; dis[S] = 0;  
+        while(!q.empty()) {  
+            int u = q.front(); q.pop(); vis[u] = 0;  
+            for(int i = head[u]; i != -1; i = edge[i].next) {  
+                int v = edge[i].to;  
+                if(edge[i].w > 0 && dis[v] > dis[u] + edge[i].c) {  
+                    dis[v] = dis[u] + edge[i].c;  
+                    pre[v] = i;  
+                    if(!vis[v]) vis[v] = 1, q.push(v);  
+                }  
+            }  
+        }  
+        return pre[T] != -1;  
+    }  
+    void doit(int S, int T, int &flow, int &cost) {
+        flow = 0; cost = 0;  
+        while(spfa(S, T)) {  
+            int x = Inf;  
+            for(int i = T; i != S; i = edge[pre[i]^1].to) x = min(x, edge[pre[i]].w);  
+            flow += x;  
+            for(int i = T; i != S; i = edge[pre[i]^1].to) {  
+                int k = pre[i];  
+                edge[k].w -= x;  
+                edge[k^1].w += x;  
+                cost += x * edge[k] .c;  
+            }  
+
+        }  
+    }  
+}