1834 [ZJOI2010]network 网络扩容

题解：先在原网络上跑最大流，然后加上带费用的边跑费用流

高一的时候做这道题怎么想不到？

注意：maxn代表的不一定是同一个变量的范围

#include<iostream>
#include<cstdio>
#include<cstring>
#include<vector>
#include<queue>
using namespace std;
const int inf=1000000000;
const int maxn=5009;

int n,m,k;

struct Edge{
	int from,to,cap,flow,cost;
};
vector<int>G[maxn];
vector<Edge>edges;
void Addedge(int x,int y,int z,int w){
	Edge e;
	e.from=x;e.to=y;e.cap=z;e.flow=0;e.cost=w;
	edges.push_back(e);
	e.from=y;e.to=x;e.cap=0;e.flow=0;e.cost=-w;
	edges.push_back(e);
	int c=edges.size();
	G[x].push_back(c-2);
	G[y].push_back(c-1);
}

int s,t,totn;
queue<int>q;
int inq[maxn];
int d[maxn];
int p[maxn];
int Spfa(int &nowflow,int &nowcost){
	for(int i=1;i<=totn;++i){
		d[i]=inf;inq[i]=0;
	}
	q.push(s);inq[s]=1;d[s]=0;
	while(!q.empty()){
		int x=q.front();q.pop();inq[x]=0;
		for(int i=0;i<G[x].size();++i){
			Edge e=edges[G[x][i]];
			if((e.cap>e.flow)&&(d[x]+e.cost<d[e.to])){
				d[e.to]=d[x]+e.cost;
				p[e.to]=G[x][i];
				if(!inq[e.to]){
					inq[e.to]=1;
					q.push(e.to);
				}
			}
		}
	}
	
	if(d[t]==inf)return 0;
	
	int x=t,a=inf;
	while(x!=s){
		Edge e=edges[p[x]];
		a=min(a,e.cap-e.flow);
		x=e.from;
	}
	nowflow+=a;nowcost+=a*d[t];
	x=t;
	while(x!=s){
		edges[p[x]].flow+=a;
		edges[p[x]^1].flow-=a;
		x=edges[p[x]].from;
	}
	return 1;
}

int rx[maxn],ry[maxn],rf[maxn],rw[maxn];
int ans,ans2;

void Minit(){
	ans=ans2=0;
	for(int i=1;i<=n+1;++i)G[i].clear();
	edges.clear();
	while(!q.empty())q.pop();
}

int main(){
	scanf("%d%d%d",&n,&m,&k);
	Minit();
	for(int i=1;i<=m;++i){
		scanf("%d%d%d%d",&rx[i],&ry[i],&rf[i],&rw[i]);
		Addedge(rx[i],ry[i],rf[i],0);
	}
	
	totn=n;s=1;t=n;
	while(Spfa(ans,ans2));
	printf("%d ",ans);
	
	Addedge(n+1,1,k,0);
	totn=n+1;s=n+1;
	for(int i=1;i<=m;++i){
		Addedge(rx[i],ry[i],inf,rw[i]);
	}
	while(Spfa(ans,ans2));
	printf("%d\n",ans2);
	return 0;
}