hdu 4744 Starloop System(zkw费用流)

              去年网赛的题，时隔这么久终于过了。。。。这题还卡普通的费用流，要用zkw费用流才能过，去年的时候太弱，费用流只是一知半解，研究了许久zkw费用流没弄明白，前两天打算再拿出来看一看，发现还是挺容易理解的，普通的费用流是拿spfa去寻找增广路，zkw费用流并不是这么找，而是利用KM算法的思想，对当前的标号找一个最小的改变量进行修改，然后每次沿着d[u]+e.cost==d[v]的路径去寻找增广路。自己YY着写了一份，过是过掉了，但是效率还是很慢。。。

代码：

#include<iostream>#include<cstdio>#include<cstring>#include<string>#include<algorithm>#include<map>#include<queue>#include<stack>#include<cmath>#include<vector>#define inf 0x3f3f3f3f#define Inf 0x3FFFFFFFFFFFFFFFLL#define eps 1e-9#define pi acos(-1.0)using namespace std;typedef long long ll;const int maxn=200+10;const int maxm=20000+10;struct Edge{    int to,cap,cost,next;    Edge(){}    Edge(int to,int cap,int cost,int next):to(to),cap(cap),cost(cost),next(next){}}edges[maxm<<1];int head[maxn],d[maxn],nEdge;bool vis[maxn];void AddEdges(int from,int to,int cap,int cost){    edges[++nEdge]=Edge(to,cap,cost,head[from]);    head[from]=nEdge;    edges[++nEdge]=Edge(from,0,-cost,head[to]);    head[to]=nEdge;}int dfs(int u,int a,int t,int &cost){    if(u==t)    {        cost+=a*d[t];        return a;    }    vis[u]=true;    int flow=0,f;    for(int k=head[u];k!=-1;k=edges[k].next)    {        Edge e=edges[k];        if(e.cap&&d[e.to]==d[u]+e.cost&&!vis[e.to])        {            f=dfs(e.to,min(a,e.cap),t,cost);            flow+=f;            edges[k].cap-=f;            edges[k^1].cap+=f;            a-=f;            if(a==0) break;        }    }    return flow;}bool changes(int n){    int mind=inf;    for(int i=0;i<=n;++i)    {        if(!vis[i]) continue;        for(int k=head[i];k!=-1;k=edges[k].next)            if(!vis[edges[k].to]&&edges[k].cap)                mind=min(mind,d[i]+edges[k].cost-d[edges[k].to]);    }    if(mind==inf) return false;    for(int i=0;i<=n;++i)        if(!vis[i]) d[i]+=mind;    return true;}struct Point{    int x,y,z,w;    void read()    {        scanf("%d%d%d%d",&x,&y,&z,&w);    }    int operator * (const Point &a) const    {        return (int)sqrt((double)(x-a.x)*(x-a.x)+(y-a.y)*(y-a.y)+(z-a.z)*(z-a.z));    }}pt[maxn];int main(){    //freopen("in.txt","r",stdin);    //freopen("out.txt","w",stdout);    int n;    while(~scanf("%d",&n))    {        if(n==0) break;        memset(head,0xff,sizeof(head));        nEdge=-1;        int sum=0;        int S=0,T=n*2+1;        for(int i=1;i<=n;++i)          pt[i].read(),sum+=pt[i].w;        for(int i=1;i<=n;++i)        {            AddEdges(S,i,pt[i].w,0);            AddEdges(i+n,T,pt[i].w,0);            for(int j=i+1;j<=n;++j)            {                int len=pt[i]*pt[j];                AddEdges(i,j+n,inf,len);                AddEdges(j,i+n,inf,len);            }        }        int flow=0,cost=0;        memset(d,0x3f,sizeof(d));        d[S]=0;        while(true)        {            memset(vis,0,sizeof(vis));            flow+=dfs(S,inf,T,cost);            if(!changes(T)) break;        }        if(flow!=sum)          printf("-1\n");        else          printf("%d\n",cost);    }    return 0;}