一道最大密度子图的模板题
一道卡精度的神题
二分精度不能太大，网络流精度不能太小 （：
//Achen
#include<algorithm>
#include<iostream>
#include<cstring>
#include<cstdlib>
#include<vector>
#include<cstdio>
#include<queue>
#include<cmath>
const int N=12007;
typedef double LL;
const LL inf=1e18,eps=1e-12;
using namespace std;
int n,m,num;
template<typename T>void read(T &x) {
char ch=getchar(); x=0; T f=1;
while(ch!=‘-‘&&(ch<‘0‘||ch>‘9‘)) ch=getchar();
if(ch==‘-‘) f=-1,ch=getchar();
for(;ch>=‘0‘&&ch<=‘9‘;ch=getchar()) x=x*10+ch-‘0‘; x*=f;
}
struct edge{
int from,to,nx;
LL cap,flow;
edge(){}
edge(int from,int to,LL cap,LL flow,int nx):from(from),to(to),cap(cap),flow(flow),nx(nx){}
}e[N];
int ecnt=1,fir[N],dd[N];
void add(int u,int v,LL cap) {
e[++ecnt]=edge(u,v,cap,0,fir[u]); fir[u]=ecnt;
e[++ecnt]=edge(v,u,0,0,fir[v]); fir[v]=ecnt;
}
queue<int>que;
int c[N],d[N],cur[N],p[N];
void bfs(int s,int t) {
for(int i=0;i<=num;i++) d[i]=num,c[i]=0;
que.push(t); d[t]=0;
while(!que.empty()) {
int x=que.front();
que.pop();
for(int i=fir[x];i;i=e[i].nx) {
int y=e[i].to;
if(d[y]==num&&e[i].cap==0) {
d[y]=d[x]+1;
que.push(y);
}
}
}
}
LL cal(int s,int t) {
LL fl=inf;
for(int i=t;i!=s;i=e[p[i]].from)
fl=min(fl,e[p[i]].cap-e[p[i]].flow);
for(int i=t;i!=s;i=e[p[i]].from) {
if(p[i]==886||((p[i]^1)==886)) {
int debug=1;
}
e[p[i]].flow=e[p[i]].flow+fl,
e[p[i]^1].flow-=fl;
}
return fl;
}
LL ISAP(int s,int t) {
bfs(s,t);
LL res=0;
for(int i=1;i<=num;i++) c[d[i]]++,cur[i]=fir[i];
for(int x=s;d[x]<num;) {
if(x==t) {
res+=cal(s,t);
x=s;
}
int ok=0;
for(int &i=cur[x];i;i=e[i].nx)
if(e[i].flow+eps<=e[i].cap&&d[e[i].to]+1==d[x]) {
ok=1; p[x=e[i].to]=i; break;
}
if(!ok) {
cur[x]=fir[x]; int M=num;
for(int i=fir[x];i;i=e[i].nx)
if(e[i].flow+eps<=e[i].cap) M=min(M,d[e[i].to]+1);
if(!(--c[d[x]])) break;
c[d[x]=M]++;
if(x!=s) x=e[p[x]].from;
}
}
return res;
}
int vis[N],ansnum;
void dfs(int x) {
for(int i=fir[x];i;i=e[i].nx)
if(!vis[e[i].to]&&e[i].cap-e[i].flow>=eps) {
vis[e[i].to]=1;
ansnum++;
dfs(e[i].to);
}
}
int ee[N][2];
int ck(LL mid,int o) {
int s=n+1,t=n+2,res=0; num=t;
ecnt=1;
memset(fir,0,sizeof(fir));
for(int i=1;i<=m;i++) {
add(ee[i][0],ee[i][1],1);
add(ee[i][1],ee[i][0],1);
}
for(int i=1;i<=n;i++) {
add(s,i,(LL)m);
add(i,t,(LL)m+2.0*mid-dd[i]);
}
if(((LL)n*m-ISAP(s,t))/2.0>=eps) res=1;
if(o==1) {
memset(vis,0,sizeof(vis));
vis[s]=1; dfs(s);
}
return res;
}
int main() {
while(scanf("%d%d",&n,&m)==2) {
if( m == 0 ) {
printf("1\n1\n") ;
continue ;
}
memset(dd,0,sizeof(dd));
for(int i=1;i<=m;i++) {
read(ee[i][0]); read(ee[i][1]);
dd[ee[i][0]]++; dd[ee[i][1]]++;
}
LL l=0,r=m;
while(l+1e-5<=r) {
LL mid=(l+r)/2.0;
if(ck(mid,0)) l=mid;
else r=mid;
}
ansnum=0;
ck(l,1);
printf("%d\n",ansnum);
for(int i=1;i<=n;i++)
if(vis[i]) printf("%d\n",i);
}
return 0;
}