hdu_3549_Flow Problem(最大流)

题目连接：http://acm.hdu.edu.cn/showproblem.php?pid=3549

题意：求1到n的最大流

题解：模版题，直接上Claris的ISAP，效率是一般dfs的十倍，ORZ Claris!!!

 1 #include<cstdio>
 2 #include<algorithm>
 3 #define F(i,a,b) for(int i=a;i<=b;i++)
 4 using namespace std;
 5 const int N=20,inf=~0U>>2,M=2010;
 6 struct edge{int t,f;edge*nxt,*pair;}*g[N],*d[N],pool[M],*cur=pool;
 7 struct ISAP{
 8     int n,m,i,S,T,h[N],gap[N],maxflow;
 9     void init(int ss,int tt){for(S=ss,T=tt,cur=pool,i=1;i<=T;i++)g[i]=d[i]=NULL,h[i]=gap[i]=0;}
10     void add(int s,int t,int f){
11         edge*p=cur++;p->t=t,p->f=f,p->nxt=g[s],g[s]=p;
12         p=cur++,p->t=s,p->f=0,p->nxt=g[t],g[t]=p;
13         g[s]->pair=g[t],g[t]->pair=g[s];
14     }
15     int sap(int v,int flow){
16         if(v==T)return flow;
17         int rec=0;
18         for(edge*p=d[v];p;p=p->nxt)if(h[v]==h[p->t]+1&&p->f){
19         int ret=sap(p->t,min(flow-rec,p->f));
20         p->f-=ret;p->pair->f+=ret;d[v]=p;
21         if((rec+=ret)==flow)return flow;
22         }
23         if(!(--gap[h[v]]))h[S]=T;
24         gap[++h[v]]++;d[v]=g[v];
25         return rec;
26     }
27     int get_ans(){
28         for(gap[maxflow=0]=T,i=1;i<=T;i++)d[i]=g[i];
29         while(h[S]<T)maxflow+=sap(S,inf);
30         return maxflow;
31     }
32 }G;
33 
34 int main(){
35     int t,n,m,x,y,c,ic=1;
36     scanf("%d",&t);
37     while(t--){
38         scanf("%d%d",&n,&m);//点，边
39         G.init(1,n);
40         F(i,1,m)scanf("%d%d%d",&x,&y,&c),G.add(x,y,c);
41         printf("Case %d: %d
",ic++,G.get_ans());
42     }
43 }

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