SPOJ371 Boxes（最小费用最大流）

把球当作水。
 1 #include<cstdio>
 2 #include<cstring>
 3 #include<queue>
 4 #include<algorithm>
 5 using namespace std;
 6 #define INF (1<<30)
 7 #define MAXN 1111 
 8 #define MAXM 1111*8 
 9 struct Edge{
10     int u,v,cap,cost,next;
11 }edge[MAXM];
12 int head[MAXN];
13 int NV,NE,vs,vt;
14 
15 void addEdge(int u,int v,int cap,int cost){
16     edge[NE].u=u; edge[NE].v=v; edge[NE].cap=cap; edge[NE].cost=cost;
17     edge[NE].next=head[u]; head[u]=NE++;
18     edge[NE].u=v; edge[NE].v=u; edge[NE].cap=0; edge[NE].cost=-cost;
19     edge[NE].next=head[v]; head[v]=NE++;
20 }
21 bool vis[MAXN];
22 int d[MAXN],pre[MAXN];
23 bool SPFA(){
24     for(int i=0;i<NV;++i){
25         vis[i]=0;
26         d[i]=INF;
27     }
28     vis[vs]=1;
29     d[vs]=0;
30     queue<int> que;
31     que.push(vs);
32     while(!que.empty()){
33         int u=que.front(); que.pop();
34         for(int i=head[u]; i!=-1; i=edge[i].next){
35             int v=edge[i].v;
36             if(edge[i].cap && d[v]>d[u]+edge[i].cost){
37                 d[v]=d[u]+edge[i].cost;
38                 pre[v]=i;
39                 if(!vis[v]){
40                     vis[v]=1;
41                     que.push(v);
42                 }
43             }
44         }
45         vis[u]=0;
46     }
47     return d[vt]!=INF;
48 }
49 int MCMF(){
50     int res=0;
51     while(SPFA()){
52         int flow=INF,cost=0;
53         for(int u=vt; u!=vs; u=edge[pre[u]].u){
54             flow=min(flow,edge[pre[u]].cap);
55         }
56         for(int u=vt; u!=vs; u=edge[pre[u]].u){
57             edge[pre[u]].cap-=flow;
58             edge[pre[u]^1].cap+=flow;
59             cost+=flow*edge[pre[u]].cost;
60         }
61         res+=cost;
62     }
63     return res;
64 }
65 int main(){
66     int t,n,a;
67     scanf("%d",&t);
68     while(t--){
69         scanf("%d",&n);
70         vs=0; vt=n+1; NV=vt+1; NE=0;
71         memset(head,-1,sizeof(head));
72         for(int i=1; i<=n; ++i){
73             scanf("%d",&a);
74             addEdge(vs,i,a,0);
75             addEdge(i,vt,1,0);
76             if(i>1) addEdge(i,i-1,INF,1);
77             else addEdge(i,n,INF,1);
78             if(i<n) addEdge(i,i+1,INF,1);
79             else addEdge(i,1,INF,1);
80         }
81         printf("%d
",MCMF());    
82     }
83     return 0;
84 }