未完成存档

Posted 2020-09-29

//http://poj.org/problem?id=2117
#include <cstring>
#include <ctype.h>
#include <cstdio>
#include <cmath>
#define N 10005

void read(int &x)
{
    x=0;
    char ch=getchar();
    for(;!isdigit(ch);ch=getchar());
    for(;isdigit(ch);ch=getchar()) x=x*10+ch-‘0‘;
}
struct Edge
{
    int next,to;
    Edge (int next=0,int to=0) :next(next),to(to) {}
}edge[N<<1];
bool vis[N],cutpoint[N];
int head[N],cnt=-1,n,m,dfn[N],low[N],tim;
void init()
{
    memset(head,0,sizeof(head));
    cnt=-1;
    tim=0;
    memset(dfn,0,sizeof(dfn));
    memset(vis,0,sizeof(vis));
    memset(low,0,sizeof(low)); 
}
void insert(int u,int v)
{
    edge[++cnt]=Edge(head[u],v);
    head[u]=cnt;
}
int min(int a,int b) {return a>b?b:a;}
void tarjan(int x,int pre)
{
    vis[x]=1;
    low[x]=dfn[x]=++tim;
    int sum=0;
    bool flag=false;
    for(int u=head[x];u!=-1;u=edge[u].next)
    {
        if((u^1)!=pre)
        {
            if(!vis[edge[u].to])
            {
                sum++;
                tarjan(edge[u].to);
                low[x]=min(low[x],low[edge[u].to]);
                if(low[edge[u].to]>=dfn[x]) flag=true;
            }
            else low[x]=min(low[x],dfn[edge[u].to]);
        }
    }
    if(pre==-1) if(sum>1) cutpoint[x]=true;
    else if(flag) cutpoint[x]=true;
}
int main()
{
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        init();
        for(int x,y;m--;)
        {
            read(x);
            read(y);
            insert(x,y);
            insert(y,x);
        }
        for(int i=1;i<=n;i++) if(!vis[i]) tarjan(i,-1);
    }
}