hdu 3491 Thieves

拆点+建边

//最好设源点为0,终点为2*n+1,否则H点会可能有流出,S点可能 //建边时要考虑四个点，两两之间的建边 #include <map>#include <set>#include <stack>#include <queue>#include <cmath>#include <ctime>#include <vector>#include <cstdio>#include <cctype>#include <cstring>#include <cstdlib>#include <iostream>#include <algorithm>using namespace std;#define INF 0x3f3f3f3f#define inf -0x3f3f3f3f#define lson l,m,rt<<1#define rson m+1,r,rt<<1|1#define mem0(a) memset(a,0,sizeof(a))#define mem1(a) memset(a,-1,sizeof(a))#define mem(a, b) memset(a, b, sizeof(a))typedef long long ll;const int maxn=410;struct Edge{    int from,to,cap,flow;    Edge(int u,int v,int c,int f):        from(u),to(v),cap(c),flow(f){}};struct Dinic{    int n,m,s,t;    vector<Edge>edges;    vector<int>G[maxn];    bool vis[maxn];    int d[maxn];    int cur[maxn];    void init(int n){        for(int i=0;i<=2*n+1;i++)            G[i].clear();        edges.clear();    }    void AddEdge(int from,int to,int cap){        edges.push_back(Edge(from,to,cap,0));        edges.push_back(Edge(to,from,0,0));        m=edges.size();        G[from].push_back(m-2);        G[to].push_back(m-1);    }    bool BFS(){        mem0(vis);        queue<int>Q;        Q.push(s);        d[s]=0;        vis[s]=1;        while(!Q.empty()){            int x=Q.front();            Q.pop();            for(int i=0;i<G[x].size();i++){                Edge& e=edges[G[x][i]];                if(!vis[e.to]&&e.cap>e.flow){                    vis[e.to]=1;                    d[e.to]=d[x]+1;                    Q.push(e.to);                }            }        }        return vis[t];    }    int DFS(int x,int a){        if(x==t||a==0)            return a;        int flow=0,f;        for(int& i=cur[x];i<G[x].size();i++){            Edge& e=edges[G[x][i]];            if(d[x]+1==d[e.to]&&(f=DFS(e.to,min(a,e.cap-e.flow)))>0){                e.flow+=f;                edges[G[x][i]^1].flow-=f;                flow+=f;                 a-=f;                if(a==0)                    break;            }        }        return flow;    }    int Maxflow(int s,int t){        this->s=s;        this->t=t;        int flow=0;        while(BFS()){            mem0(cur);            flow+=DFS(s,INF);        }        return flow;    }};Dinic ZYC;int main(){    int t,n,m,S,H,x;    scanf("%d",&t);    while(t--){        scanf("%d%d%d%d",&n,&m,&S,&H);        ZYC.init(n);        for(int i=1;i<=n;i++){            scanf("%d",&x);            if(i!=S&&i!=H){                ZYC.AddEdge(i,i+n,x);            }            else                ZYC.AddEdge(i,i+n,INF);        }        ZYC.AddEdge(0,S,INF);        ZYC.AddEdge(H+n,2*n+1,INF);        int a,b;        while(m--){            scanf("%d%d",&a,&b);            ZYC.AddEdge(a+n,b,INF);            ZYC.AddEdge(b+n,a,INF);        }        printf("%d\n",ZYC.Maxflow(0,2*n+1));    }    return 0;}