BZOJ2657: [Zjoi2012]旅游(journey)

#include<cstdio>
#include<iostream>
#include<cstring>
#include<map>
using namespace std;
#define Side side
struct side
{
int x,y;
inline friend bool operator <(Side a,Side b)
{
return min(a.x,a.y)<min(b.x,b.y)||(min(a.x,a.y)==min(b.x,b.y)&&max(a.x,a.y)<max(b.x,b.y));
}
};
map<side,int>Q;
int f[2100001];
int g[2100001];
char c;
inline void read(int &a)
{
a=0;do c=getchar();while(c<'0'||c>'9');
while(c<='9'&&c>='0')a=(a<<3)+(a<<1)+c-'0',c=getchar();
}
struct Chain
{
Chain *next;
int u;
Chain(){next=NULL;}
}*Head[2000001];
inline void addside(int a,int b)
{Chain *tp=new Chain;tp->next=Head[a];Head[a]=tp;tp->u=b;}
int tot;

void DFS(int u,int fa)
{
int max=0,sec=0;
for(Chain*tp=Head[u];tp;tp=tp->next)
if(tp->u!=fa)
{
DFS(tp->u,u);
if(f[tp->u]>max)
sec=max,max=f[tp->u];
else if(f[tp->u]>sec)sec=f[tp->u];
}
f[u]=max+1;
g[u]=sec+1+max;
}

int main()
{
int n;
scanf("%d",&n);
n-=2;
Side tp;
int a,b,c;
for(int i=1;i<=n;i++)
{
++tot;
read(a),read(b),read(c);
tp.x=a,tp.y=b;
if(Q[tp])
addside(Q[tp],tot),
addside(tot,Q[tp]);
else
Q[tp]=tot;

tp.y=c;
if(Q[tp])
addside(Q[tp],tot),
addside(tot,Q[tp]);
else
Q[tp]=tot;

tp.x=b;
if(Q[tp])
addside(Q[tp],tot),
addside(tot,Q[tp]);
else
Q[tp]=tot;

}

DFS(1,1);
int ans=-1;
for(int i=1;i<=tot;i++)
ans=max(ans,f[i]),ans=max(ans,g[i]);
printf("%d\n",ans);
return 0;
}