luogu1345 奶牛的電信

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　　拆點、最小割的模板題。

　　我只想說一點。拆點時不可以下意識地初始化！起點和終點不能直接寫編號！寫拆點後的Id！

#include <cstdio>#include <cstring>#include <algorithm>#include <queue>using namespace std;#define In(x) (x) * 2 - 1#define Out(x) (x) * 2const int MAX_NODE = 210, MAX_EDGE = 210 * 210 * 2, INF = 0x3f3f3f3f;struct Dinic{private:    struct Node;    struct Edge;    struct Node    {        Edge *Head, *DfsFrom;        int Level;    }_nodes[MAX_NODE], *Start, *Target;    int TotNode;    struct Edge    {        Node *To;        Edge *Next, *Rev;        int Cap;    }_edges[MAX_EDGE];    int _eCount;    Edge *AddEdge(Node *from, Node *to, int cap)    {        Edge *e = _edges + ++_eCount;        e->To = to;        e->Cap = cap;        e->Next = from->Head;        from->Head = e;        return e;    }    bool Bfs()    {        for (int i = 1; i <= TotNode; i++)            _nodes[i].Level = 0;        Start->Level = 1;        static queue<Node*> q;        q.push(Start);        while (!q.empty())        {            Node *cur = q.front();            q.pop();            for (Edge *e = cur->Head; e; e = e->Next)            {                if (e->Cap && !e->To->Level)                {                    e->To->Level = cur->Level + 1;                    q.push(e->To);                }            }        }        return Target->Level;    }    int Dfs(Node *cur, int limit)    {        if (cur == Target)            return limit;        if (limit == 0)            return 0;        int curTake = 0;        for (Edge *e = cur->DfsFrom; e; e = (cur->DfsFrom) = e->Next)        {            if (e->Cap && e->To->Level == cur->Level + 1)            {                int nextTake = Dfs(e->To, min(limit - curTake, e->Cap));                curTake += nextTake;                e->Cap -= nextTake;                e->Rev->Cap += nextTake;            }            if (curTake == limit)                break;        }        return curTake;    }public:    void Init(int n, int s, int t)    {        TotNode = n;        Start = _nodes + s;        Target = _nodes + t;    }    void Build(int uId, int vId, int cap)    {        Node *u = _nodes + uId, *v = _nodes + vId;        Edge *e1 = AddEdge(u, v, cap), *e2 = AddEdge(v, u, 0);        e1->Rev = e2;        e2->Rev = e1;    }    int MaxFlow()    {        int ans = 0;        while (Bfs())        {            for (int i = 1; i <= TotNode; i++)                _nodes[i].DfsFrom = _nodes[i].Head;            ans += Dfs(Start, INF);        }        return ans;    }}g;int main(){    int totNode, totEdge, s, t;    scanf("%d%d%d%d", &totNode, &totEdge, &s, &t);    g.Init(totNode * 2, Out(s), In(t));//！！！！！！！！！！！！！！！！！！！！！！！！！！    for (int i = 1; i <= totNode; i++)        g.Build(In(i), Out(i), 1);    for (int i = 1; i <= totEdge; i++)    {        int u, v;        scanf("%d%d", &u, &v);        g.Build(Out(u), In(v), INF);        g.Build(Out(v), In(u), INF);    }    printf("%d\n", g.MaxFlow());    return 0;}

　　

luogu1345 奶牛的電信