POJ2942 Knights of the Round Table[点双连通分量|二分图染色|补图]

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#define C(x) memset(x,0,sizeof(x))
using namespace std;
const int N=1005,M=1e6+5;
inline int read(){
    char c=getchar();int x=0,f=1;
    while(c<‘0‘||c>‘9‘){if(c==‘-‘)f=-1;c=getchar();}
    while(c>=‘0‘&&c<=‘9‘){x=x*10+c-‘0‘;c=getchar();}
    return x*f;
}
int n=0,m,u,v,g[N][N];
struct edge{
    int v,ne;
}e[M<<1];
int h[N],cnt=0;
inline void ins(int u,int v){
    cnt++;
    e[cnt].v=v;e[cnt].ne=h[u];h[u]=cnt;
    cnt++;
    e[cnt].v=u;e[cnt].ne=h[v];h[v]=cnt;
}
void buildGraph(){
    memset(h,0,sizeof(h)); cnt=0;
    for(int i=1;i<=n;i++)
        for(int j=i+1;j<=n;j++) if(!g[i][j]) ins(i,j);
}
struct data{
    int u,v;
    data(int a=0,int b=0):u(a),v(b){}
}st[M<<1];
int top=0;
int dfn[N],low[N],iscut[N],belong[N],dfc=0,bcc=0;
int col[N],ok[N];
bool color(int u,int id){//printf("%d %d %d\n",u,col[u],id);
    for(int i=h[u];i;i=e[i].ne){
        int v=e[i].v;
        if(belong[v]!=id) continue;
        if(col[v]==col[u]) return 0;//first do this
        if(!col[v]){
            col[v]=3-col[u];
            if(!color(v,id)) return 0;
        }
    }
    return 1;
}
void dfs(int u,int fa){
    dfn[u]=low[u]=++dfc;
    int child=0;
    for(int i=h[u];i;i=e[i].ne){
        int v=e[i].v;
        if(!dfn[v]){
            st[++top]=data(u,v);
            child++;
            dfs(v,u);
            low[u]=min(low[u],low[v]);
            if(low[v]>=dfn[u]){
                iscut[u]=1;
                bcc++;
                while(true){
                    int tu=st[top].u,tv=st[top--].v;
                    if(belong[tu]!=bcc) belong[tu]=bcc;
                    if(belong[tv]!=bcc) belong[tv]=bcc;
                    if(tu==u&&tv==v) break;
                }
                col[u]=1;
                if(!color(u,bcc))
                    for(int i=1;i<=n;i++) if(belong[i]==bcc) ok[i]=1;
                col[u]=0;//for cut vertex
            }
        }else if(dfn[v]<dfn[u]&&v!=fa){
            st[++top]=data(u,v);//notice!!!
            low[u]=min(low[u],dfn[v]);
        }
    }
    if(child==1&&fa==0) iscut[u]=0;
}
void BCC(){
    dfc=bcc=0;top=0;
    C(dfn);C(low);C(iscut);C(belong);
    C(col);C(ok);
    for(int i=1;i<=n;i++) if(!dfn[i]) dfs(i,0);
}
int main(){
    while(scanf("%d%d",&n,&m)!=EOF&&(n||m)){
        memset(g,0,sizeof(g));
        for(int i=1;i<=m;i++){u=read();v=read();g[u][v]=g[v][u]=1;}
        buildGraph();
        BCC();
        int ans=0;
        for(int i=1;i<=n;i++) if(!ok[i]) ans++;
        printf("%d\n",ans);
    }
}