bzoj 1040: [ZJOI2008]骑士 環套樹DP

#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<ctime>
#include<cmath>
#include<algorithm>
#include<set>
#include<map>
#include<vector>
#include<string>
#include<queue>
using namespace std;
#ifdef WIN32
#define LL "%I64d"
#else
#define LL "%lld"
#endif
#define MAXN 1100000
#define MAXV MAXN*2
#define MAXE MAXV*2
#define INF 0x3f3f3f3f
#define INFL 0x00003f3f3f3f3f3fLL
typedef long long qword;
inline int nextInt()
{
        char ch;
        int x=0;
        bool flag=false;
        do
                ch=getchar(),flag=(ch==‘-‘)?true:flag;
        while(ch<‘0‘||ch>‘9‘);
        do x=x*10+ch-‘0‘;
        while (ch=getchar(),ch<=‘9‘ && ch>=‘0‘);
        return x*(flag?-1:1);
}

int n,m;
int e[MAXN][3];
struct Edge
{
        int np;
        Edge *next;
}E[MAXE],*V[MAXV];
int tope=-1;
void addedge(int x,int y)
{
        E[++tope].np=y;
        E[tope].next=V[x];
        V[x]=&E[tope];
}
int uf[MAXN];
int get_fa(int now)
{
        return (now==uf[now])?now:(uf[now]=get_fa(uf[now]));
}
bool comb(int x,int y)
{
        x=get_fa(x);
        y=get_fa(y);
        if (x==y)return false;
        uf[x]=y;
        return true;
}
int roof[MAXN],topr=-1;
int state[MAXN];
int ptr[MAXN];
int v[MAXN];
pair<qword,qword> dfs(int now,int f)
{
        pair<qword,qword> ret,t;
        Edge *ne;
        ret=make_pair(v[now],0);
        for (ne=V[now];ne;ne=ne->next)
        {
                if (ne->np==f)continue;
                t=dfs(ne->np,now);
                ret.second+=max(t.first,t.second);
                ret.first+=t.second;
        }
        if (state[now])ret.first=-INFL;
        return ret;
}
int main()
{        int i,j,k;
        int x,y,z;
        qword ans=0;
        scanf("%d",&n);
        memset(ptr,-1,sizeof(ptr));
        for (i=0;i<=n;i++)uf[i]=i;
        for (i=0;i<n;i++)
        {
                scanf("%d%d",&v[i+1],&e[i][1]);
                e[i][0]=i+1;
                if (!comb(e[i][0],e[i][1]))
                {
                        roof[++topr]=e[i][0];
                        e[i][2]=true;
                        ptr[e[i][0]]=e[i][1];
                }else
                {
                        addedge(e[i][0],e[i][1]);
                        addedge(e[i][1],e[i][0]);
                }
        }
        for (i=0;i<=topr;i++)
        {
                state[get_fa(roof[i])]=true;
        }
        for (i=1;i<=n;i++)
        {
                if (!state[get_fa(i)])
                {
                        state[get_fa(i)]=true;
                        roof[++topr]=get_fa(i);
                }
        }
        memset(state,0,sizeof(state));
        pair<qword,qword> pr;
        qword t;
        for (i=0;i<=topr;i++)
        {
                if (ptr[roof[i]]==-1)
                {
                        pr=dfs(roof[i],roof[i]);
                        ans+=max(pr.first,pr.second);
                }else
                {
                        //state[roof[i]]=true;
                        state[ptr[roof[i]]]=true;
                        pr=dfs(roof[i],roof[i]);
                        t=max(pr.first,pr.second);
                        state[ptr[roof[i]]]=false;
                        pr=dfs(roof[i],roof[j]);
                        t=max(t,pr.second);
                        ans+=t;
                }
        }
        printf(LL"\n",ans);
        return 0;
}