zoj 3885 The Exchange of Items 最小用费最大流

#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[i]=inf;    memset(inq,0,sizeof(inq));    d[s]=0;    inq[s]=1;    p[s]=0;    a[s]=inf;    queue<int>Q;    Q.push(s);    while(!Q.empty())    {        u=Q.front();        Q.pop();        inq[u]=0;        for(i=0; i<G[u].size(); i++)        {            Edge &e=edges[G[u][i]];            if(e.cap>e.flow&&d[e.to]>d[u]+e.cost)            {                d[e.to]=d[u]+e.cost;                p[e.to]=G[u][i];                a[e.to]=min(a[u],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[u]].flow+=a[t];        edges[p[u]^1].flow-=a[t];        u=edges[p[u]].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][i]].cap!=edges[G[0][i]].flow) cost=-1;    for(i=1;i<=n;i++)        for(j=0;j<G[i].size();j++)    {        if(edges[G[i][j]].to==t&&edges[G[i][j]].cap!=edges[G[i][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[i].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;}