HDU 4411 Arrest

Posted 2020-07-29 GFY

http://www.cnblogs.com/jianglangcaijin/archive/2012/09/24/2700509.html

思路:

S->0 流量为K费用0

0->i 流量为inf,费用为a[0][i]

0->T 流量为K，费用0

i->i+n 流量为1,费用为-inf

i+n->T 流量为1，费用为a[0][i]

 1 #include<algorithm>
 2 #include<cstdio>
 3 #include<cmath>
 4 #include<cstring>
 5 #include<iostream>
 6 #define inf 1000000
 7 int a[505][505],K;
 8 int tot,go[200005],next[200005],first[200005],cost[200005],flow[200005];
 9 int op[200005],dis[200005],c[200005],vis[200005],edge[200005],from[200005];
10 int S,T,n,m,ans;
11 int read(){
12     char ch=getchar();int t=0,f=1;
13     while (ch<\'0\'||ch>\'9\'){if (ch==\'-\') f=-1;ch=getchar();}
14     while (\'0\'<=ch&&ch<=\'9\'){t=t*10+ch-\'0\';ch=getchar();}
15     return t*f;
16 }
17 void insert(int x,int y,int z,int l){
18     tot++;
19     go[tot]=y;
20     next[tot]=first[x];
21     first[x]=tot;
22     flow[tot]=z;
23     cost[tot]=l;
24 }
25 void add(int x,int y,int z,int l){
26     insert(x,y,z,l);op[tot]=tot+1;
27     insert(y,x,0,-l);op[tot]=tot-1;
28 }
29 bool spfa(){
30     for (int i=0;i<=T;i++)
31      dis[i]=0x3f3f3f3f,vis[i]=0;
32     int h=1,t=1;c[1]=S;vis[S]=1;dis[S]=0;
33     while (h<=t){
34         int now=c[h++];
35         for (int i=first[now];i;i=next[i]){
36             int pur=go[i];
37             if (dis[pur]>dis[now]+cost[i]&&flow[i]){
38                 dis[pur]=dis[now]+cost[i];
39                 edge[pur]=i;
40                 from[pur]=now;
41                 if (vis[pur]) continue;
42                 vis[pur]=1;
43                 c[++t]=pur;
44             }
45         }
46         vis[now]=0;
47     }
48     return dis[T]!=0x3f3f3f3f;
49 }
50 void updata(){
51     int mn=0x3f3f3f3f;
52     for (int i=T;i!=S;i=from[i]){
53         mn=std::min(mn,flow[edge[i]]);
54     }
55     for (int i=T;i!=S;i=from[i]){
56         ans+=mn*cost[edge[i]];
57         flow[edge[i]]-=mn;
58         flow[op[edge[i]]]+=mn;
59     }
60 }
61 int main(){
62     while (scanf("%d",&n)!=EOF){
63         m=read();K=read();
64         if (n==0&&K==0&&m==0) return 0;
65         for (int i=0;i<=T;i++) first[i]=0;tot=0;
66         S=2*n+1;T=S+1;
67         for (int i=0;i<=n;i++)
68          for (int j=0;j<=n;j++)
69           if (i==j) a[i][j]=0;
70           else a[i][j]=0x3f3f3f3f;
71         while(m--){
72             int u=read(),v=read(),w=read();
73             a[u][v]=std::min(a[u][v],w);
74             a[v][u]=std::min(a[v][u],w);
75         }
76         for (int k=0;k<=n;k++)
77          for (int i=0;i<=n;i++)
78           for (int j=0;j<=n;j++)
79            a[i][j]=std::min(a[i][j],a[i][k]+a[k][j]);
80         add(S,0,K,0);
81         add(0,T,K,0);
82         for (int i=1;i<=n;i++)
83          if (a[0][i]<0x3f3f3f3f)
84           add(0,i,inf,a[0][i]);
85         for (int i=1;i<=n;i++)
86          for (int j=i+1;j<=n;j++)
87           if (a[i][j]<0x3f3f3f3f)
88            add(i+n,j,1,a[i][j]);
89         for (int i=1;i<=n;i++)
90           if (a[0][i]<0x3f3f3f3f)
91            add(i+n,T,1,a[0][i]);
92         for (int i=1;i<=n;i++)
93          add(i,i+n,1,-inf);      
94         ans=inf*n;
95         while (spfa()) updata();
96         printf("%d\\n",ans);  
97     }
98 }