zoj 3885 The Exchange of Items 最小费用最大流

jlthlx

#include<stdio.h>
#include<string.h>
#include<vector>
#include<queue>
#include<algorithm>
using namespace std;
const int N=256;
const int inf=0x7fffffff;
struct Edge
{
int from,to,cap,flow,cost;
};
vector<Edge>edges;
vector<int>G[N];
int n,m;
int inq[N],p[N],d[N],a[N];
void AddEdge(int from, int to,int cap, int cost)
{
Edge tp;
tp.from=from,tp.to=to,tp.cap=cap,tp.flow=0,tp.cost=cost;
edges.push_back(tp);
tp.from=to,tp.to=from,tp.cap=0,tp.flow=0,tp.cost=-cost;
edges.push_back(tp);
int g=edges.size();
G[from].push_back(g-2);
G[to].push_back(g-1);
}
int BellmanFord(int s,int t,int &flow, int &cost)
{
int i,j,u;
for(i=0; i<=n+1; i++) d=inf;
memset(inq,0,sizeof(inq));
d=0;
inq=1;
p=0;
a=inf;
queue<int>Q;
Q.push(s);
while(!Q.empty())
{
u=Q.front();
Q.pop();
inq=0;
for(i=0; i<G.size(); i++)
{
Edge &e=edges[G];
if(e.cap>e.flow&&d[e.to]>d+e.cost)
{
d[e.to]=d+e.cost;
p[e.to]=G;
a[e.to]=min(a,e.cap-e.flow);
if(!inq[e.to])
{
Q.push(e.to);
inq[e.to]=1;
}
}
}
}
if(d[t]==inf) return 0;
flow+=a[t];
cost+=d[t]*a[t];
u=t;
while(u!=0)
{
edges[p].flow+=a[t];
edges[p^1].flow-=a[t];
u=edges[p].from;
}
return 1;
}
void Mincost(int s,int t)
{
int i,j,flow=0,cost=0;
while(BellmanFord(s,t,flow,cost));
//printf("%d\n",cost);
for(i=0;i<G[0].size();i++)
if(edges[G[0]].cap!=edges[G[0]].flow) cost=-1;
for(i=1;i<=n;i++)
for(j=0;j<G.size();j++)
{
if(edges[G[j]].to==t&&edges[G[j]].cap!=edges[G[j]].flow) cost=-1;
}
printf("%d\n",cost);
}
int main()
{
int i,u,v,a,b;
while(~scanf("%d%d",&n,&m))
{
for(i=0; i<=n+1; i++) G.clear();
edges.clear();
for(i=1;i<=n;i++)
{
scanf("%d%d",&a,&b);
if(a>b) AddEdge(i,n+1,a-b,0);
else if(b>a) AddEdge(0,i,b-a,0);
}
for(i=0;i<m;i++)
{
scanf("%d%d",&u,&v);
AddEdge(u,v,100000+5,1);
AddEdge(v,u,100000+5,1);
}
Mincost(0,n+1);
}
return 0;
}