BZOJ4871 Shoi2017摧毁“树状图”（树形dp）

　　设f[i][0/1/2/3/4/5]表示i子树中选一条链不包含根/i子树中选一条链包含根但不能继续向上延伸/i子树中选一条链可以继续向上延伸/选两条链不包含根/选两条链包含根但不能继续向上延伸/选两条链能继续向上延伸，大力讨论即可。代码看起来很(mo)有(ming)意(qi)思(miao)。

#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstdlib>
#include<cstring>
#include<algorithm>
using namespace std;
#define ll long long
#define N 500010
char getc(){char c=getchar();while ((c<'A'||c>'Z')&&(c<'a'||c>'z')&&(c<''||c>'')) c=getchar();return c;}
int gcd(int n,int m){return m==?n:gcd(m,n%m);}
int read()
{
    int x=,f=;char c=getchar();
    while (c<''||c>'') {if (c=='-') f=-;c=getchar();}
    while (c>=''&&c<='') x=(x<<)+(x<<)+(c^),c=getchar();
    return x*f;
}
int T,n,p[N],f[N][],t;
int mx[][];
struct data{int to,nxt;
}edge[N<<];
void addedge(int x,int y){t++;edge[t].to=y,edge[t].nxt=p[x],p[x]=t;}
inline void up(int &x,int y){x=max(x,y);}
inline int max(int x,int y,int z){return max(max(x,y),z);}
void update(int x)
{
    for (int i=;i<;i++)
        for (int j=;j<;j++)
        if (f[x][i]>f[mx[j][i]][i])
        {
            for (int k=;k>j;k--) mx[k][i]=mx[k-][i];
            mx[j][i]=x;break;
        }
}
int findmx(int x){return f[mx[][x]][x];}
int findmx(int x,int y)
{
    if (mx[][x]!=mx[][y]) return f[mx[][x]][x]+f[mx[][y]][y];
    return max(f[mx[][x]][x]+f[mx[][y]][y],f[mx[][x]][x]+f[mx[][y]][y]);
}
int findmx(int x,int y,int z)
{
    int s=-n;
    for (int i=;i<;i++)
        for (int j=i+;j<;j++)
            for (int k=;k<;k++)
            if (mx[k][z]!=mx[i][x]&&mx[k][z]!=mx[j][y]) up(s,f[mx[k][z]][z]+f[mx[i][x]][x]+f[mx[j][y]][y]);
    return s;
}
int findmx(int a,int b,int c,int d){return f[mx[][a]][a]+f[mx[][b]][b]+f[mx[][c]][c]+f[mx[][d]][d];}
void dfs(int k,int from)
{
    int son=;
    for (int i=p[k];i;i=edge[i].nxt)
    if (edge[i].to!=from) son++,dfs(edge[i].to,k);
    memset(mx,,sizeof(mx));
    for (int i=p[k];i;i=edge[i].nxt)
    if (edge[i].to!=from) update(edge[i].to);
    f[k][]=max(findmx(),findmx()+,findmx()+);
    f[k][]=findmx(,)+son-;
    f[k][]=max(son,findmx()+son-);
    f[k][]=max(findmx(),findmx()+,findmx()+);
    for (int i=;i<;i++)
        for (int j=i;j<;j++)
        up(f[k][],findmx(i,j)+-(i==)-(j==));
    f[k][]=max(findmx(,,,)-,max(findmx(,,)-,findmx(,,)-),findmx(,)-)+son;
    f[k][]=max(max(findmx()-,findmx(,,)-,max(findmx(,),findmx(,),findmx(,))-),max(findmx(),findmx(),findmx())-)+son;
}
int main()
{
#ifndef ONLINE_JUDGE
    freopen("bzoj4871.in","r",stdin);
    freopen("bzoj4871.out","w",stdout);
    const char LL[]="%I64d\n";
#else
    const char LL[]="%lld\n";
#endif
    T=read();int op=read();
    while (T--)
    {
        n=read();if (op>=) read(),read();if (op==) read(),read();
        t=;for (int i=;i<=n;i++) p[i]=;
        f[][]=f[][]=f[][]=f[][]=f[][]=f[][]=-n;
        for (int i=;i<n;i++)
        {
            int x=read(),y=read();
            addedge(x,y),addedge(y,x);
        }
        dfs(,);
        printf("%d\n",max(max(f[][],f[][],f[][]),max(f[][],f[][],f[][])));
    }
    return ;
}