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