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!!!

#include<cstdio>
#include<algorithm>
#define F(i,a,b) for(int i=a;i<=b;i++)
using namespace std;
const int N=20,inf=~0U>>2,M=2010;
struct edge{int t,f;edge*nxt,*pair;}*g[N],*d[N],pool[M],*cur=pool;
struct ISAP{
    int n,m,i,S,T,h[N],gap[N],maxflow;
    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;}
    void add(int s,int t,int f){
        edge*p=cur++;p->t=t,p->f=f,p->nxt=g[s],g[s]=p;
        p=cur++,p->t=s,p->f=0,p->nxt=g[t],g[t]=p;
        g[s]->pair=g[t],g[t]->pair=g[s];
    }
    int sap(int v,int flow){
        if(v==T)return flow;
        int rec=0;
        for(edge*p=d[v];p;p=p->nxt)if(h[v]==h[p->t]+1&&p->f){
        int ret=sap(p->t,min(flow-rec,p->f));
        p->f-=ret;p->pair->f+=ret;d[v]=p;
        if((rec+=ret)==flow)return flow;
        }
        if(!(--gap[h[v]]))h[S]=T;
        gap[++h[v]]++;d[v]=g[v];
        return rec;
    }
    int get_ans(){
        for(gap[maxflow=0]=T,i=1;i<=T;i++)d[i]=g[i];
        while(h[S]<T)maxflow+=sap(S,inf);
        return maxflow;
    }
}G;

int main(){
    int t,n,m,x,y,c,ic=1;
    scanf("%d",&t);
    while(t--){
        scanf("%d%d",&n,&m);//点，边
        G.init(1,n);
        F(i,1,m)scanf("%d%d%d",&x,&y,&c),G.add(x,y,c);
        printf("Case %d: %d
",ic++,G.get_ans());
    }
}