bzoj1124: [POI2008]枪战Maf

#include<cstdio>
#include<iostream>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<cmath>
#include<vector>
using namespace std;
int read()
{
    int x=0,f=1;char ch=getchar();
    while(ch<‘0‘||‘9‘<ch){if(ch==‘-‘)f=-1;ch=getchar();}
    while(‘0‘<=ch&&ch<=‘9‘){x=x*10+ch-‘0‘;ch=getchar();}
    return x*f;
}

struct node
{
    int x,y,next;
}a[2100000];int len,last[1100000];
void ins(int x,int y)
{
    len++;
    a[len].x=x;a[len].y=y;
    a[len].next=last[x];last[x]=len;
}

vector<int>h;
int z,ys[1100000],fa[1100000];
bool v[1100000];
void findhuan(int x)
{
    ys[x]=++z;
    if(v[x]==true)h.push_back(x);
    for(int k=last[x];k;k=a[k].next)
    {
        int y=a[k].y;
        if(ys[y]==0)
        {
            fa[y]=x;
            findhuan(y);
        }
    }
    for(int k=last[x];k;k=a[k].next)
    {
        int y=a[k].y;
        if(ys[y]>ys[x]&&fa[y]!=x)
        {
            h.push_back(y);v[y]=true;
            do
            {
                y=fa[y];v[y]=true;
                h.push_back(y);
            }while(y!=x);
        }
    }
}
int mmin,cc,tot[1100000];bool bekilled[1100000];
int dfs(int x,int fr,bool bk)
{
    tot[x]=1;
    for(int k=last[x];k;k=a[k].next)
    {
        int y=a[k].y;
        if(v[y]==false&&y!=fr)
        {
            bk=true;
            dfs(y,x,false);
            tot[x]+=tot[y];
        }
    }
    if(bk==false)cc++;
    if(bekilled[x]==false&&fr!=-1)
    {
        if(bekilled[fr]==false)
        {
            mmin++;
            bekilled[fr]=true;
        }
    }
}

int c[1100000];
int main()
{
    freopen("a.in","r",stdin);
    freopen("a.out","w",stdout);
    int n;
    n=read();
    len=0;memset(last,0,sizeof(last));
    memset(v,false,sizeof(v));
    for(int i=1;i<=n;i++)
    {
        c[i]=read();
        ins(i,c[i]);ins(c[i],i);
        if(c[c[i]]==i)v[i]=v[c[i]]=true;
    }
    
    z=0;int mmax=0;mmin=0;
    memset(bekilled,false,sizeof(bekilled));
    for(int i=1;i<=n;i++)
    {
        if(ys[i]==0)
        {
            h.clear();
            fa[i]=i;findhuan(i);
            int leaf=0,stot=0;
            for(int j=0;j<h.size();j++)
            {
                int k=h[j];
                cc=0;dfs(k,-1,true);
                stot+=tot[k];
                leaf+=cc;
            }
            if(leaf==0&&stot!=1)leaf=1;
            mmax+=stot-leaf;
            
            if(h.size()==1&&bekilled[h[0]]==false)mmin++;
            else if(h.size()==2)
            {
                if(!(bekilled[h[0]]|bekilled[h[1]]))mmin++;
            }
            else
            {
                int H=h.size();bool ay=false;
                for(int j=0;j<H;j++)
                    if(bekilled[h[j]])ay=true;
                    
                if(ay==false)mmin+=(h.size()+1)/2;
                else
                {
                    int zz=2;
                    while(zz--)
                    {
                        for(int j=0;j<H;j++)
                        {
                            if(bekilled[h[j]]&&!bekilled[h[(j+1)%H]]&&!bekilled[h[(j+2)%H]])
                            {
                                bekilled[h[(j+2)%H]]=true;mmin++;
                            }
                        }
                    }
                }
            }
        }
    }
    printf("%d %d\n",mmin,mmax);
    return 0;
}