# POJ3155 Hard Life

https://vjudge.net/problem/POJ-3155

  1 #include<cstdio>
2 #include<cstring>
3 #include<cstdlib>
4 #include<algorithm>
5 //#include<iostream>
6 using namespace std;
7 #define LL long long
8
9 int n,m;
10 #define maxn 111
11 #define maxm 1011*4+maxn*4
12 #define eps 1e-5
13 struct NetEdge{int to,next; double cap,flow;};
14 struct Net
15 {
16     int n,le,s,t,first[maxn],dis[maxn],cur[maxn],que[maxn],head,tail; NetEdge edge[maxm]; bool vis[maxn];
17     void clear(int N) {n=N; le=2; memset(first,0,sizeof(first));}
18     void in(int x,int y,double c) {NetEdge &e=edge[le]; e.to=y; e.cap=c; e.flow=0; e.next=first[x]; first[x]=le++;}
19     void insert(int x,int y,double c) {in(x,y,c); in(y,x,0);}
20     bool bfs()
21     {
22         memset(dis,0,sizeof(dis));
25         {
27             for (int i=first[x];i;i=edge[i].next)
28             {
29                 NetEdge &e=edge[i]; if (dis[e.to] || e.cap-e.flow<eps) continue;
30                 dis[e.to]=dis[x]+1; que[tail++]=e.to;
31             }
32         }
33         return dis[t]>0;
34     }
35     double dfs(int x,double a)
36     {
37         if (x==t || a<eps) return a;
38         double flow=0,f;
39         for (int &i=cur[x];i;i=edge[i].next)
40         {
41             NetEdge &e=edge[i];
42             if (dis[e.to]==dis[x]+1 && (f=dfs(e.to,min(a,e.cap-e.flow)))>eps)
43             {
44                 e.flow+=f;
45                 flow+=f;
46                 edge[i^1].flow-=f;
47                 a-=f;
48                 if (a<eps) break;
49             }
50         }
51         return flow;
52     }
53     double Dinic(int S,int T)
54     {
55         s=S; t=T;
56         double flow=0;
57         while (bfs())
58         {
59             for (int i=1;i<=n;i++) cur[i]=first[i];
60             flow+=dfs(s,0x3f3f3f3f);
61         }
62         return flow;
63     }
64     void dfs2(int x)
65     {
66         vis[x]=1;
67         for (int i=first[x];i;i=edge[i].next)
68             if (!vis[edge[i].to] && edge[i^1].cap-edge[i^1].flow>eps) dfs2(edge[i].to);
69     }
70 }g,g2;
71
72 int du[maxn],lans,ans[maxn];
73 int main()
74 {
75     scanf("%d%d",&n,&m);
76     g.clear(n+2);
77     memset(du,0,sizeof(du));
78     for (int i=1,x,y;i<=m;i++)
79     {
80         scanf("%d%d",&x,&y);
81         g.insert(x,y,1); g.insert(y,x,1);
82         du[x]++; du[y]++;
83     }
84     for (int i=1;i<=n;i++) g.insert(n+1,i,m);
85     double L=0,R=(n-1)>>1;
86     while (R-L>1e-7)
87     {
88         double mid=(L+R)/2.;
89         g2=g;
90         for (int i=1;i<=n;i++) g2.insert(i,n+2,m+2*mid-du[i]);
91         if (m*n-g2.Dinic(n+1,n+2)>eps) L=mid+1e-7;
92         else R=mid;
93     }
94
95     g2=g;
96     for (int i=1;i<=n;i++) g2.insert(i,n+2,m+2*L-du[i]);
97     g2.Dinic(n+1,n+2);
98     memset(g2.vis,0,sizeof(g2.vis));
99     g2.dfs2(n+2);
100     lans=0;
101     for (int i=1;i<=n;i++) if (!g2.vis[i]) ans[++lans]=i;
102     if (lans==0) ans[++lans]=1;
103     printf("%d\n",lans);
104     for (int i=1;i<=lans;i++) printf("%d\n",ans[i]);
105     return 0;
106 }
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posted @ 2020-02-05 11:37  Blue233333  阅读(157)  评论(0编辑  收藏  举报