AC通道：http://www.lydsy.com/JudgeOnline/problem.php?id=2157

【题解】

很模板的题目。

首先还是把边建成点（这是一种套路），然后上LCT维护就行了。

这题还有一个启示：在打标记时要直接下传一次，否则会出现查询时还没有下传标记的情况。

#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<ctime>
#include<cmath>
#include<algorithm>
using namespace std;
#define FILE "read"
#define MAXN 40010
#define INF 1000000000
#define up(i,j,n) for(int i=j;i<=n;++i)
#define dn(i,j,n) for(int i=j;i>=n;--i)
#define cmax(a,b) a=max(a,b)
#define cmin(a,b) a=min(a,b)
inline int read(){
	int x=0,f=1;  char ch=getchar();
	while(!isdigit(ch))  {if(ch=='-')  f=-1;  ch=getchar();}
	while(isdigit(ch))  {x=x*10+ch-'0';  ch=getchar();}
	return x*f;
}
int n,m,cnt,id[MAXN];
namespace Link_Cut_Tree{
	int f[MAXN],vis[MAXN],stack[MAXN],tag[MAXN],v[MAXN],sum[MAXN],maxx[MAXN],minn[MAXN],son[MAXN][2];
	bool get(int x){return son[f[x]][1]==x;}
	bool isroot(int x){return son[f[x]][0]!=x&&son[f[x]][1]!=x;}
	void updata(int x){
		sum[x]=sum[son[x][0]]+sum[son[x][1]]+v[x];
		maxx[x]=max(maxx[son[x][0]],maxx[son[x][1]]);
		minn[x]=min(minn[son[x][0]],minn[son[x][1]]);
		if(x>n)cmax(maxx[x],v[x]),cmin(minn[x],v[x]);
	}
	void rever(int x){
		sum[x]=-sum[x];v[x]=-v[x];
		swap(minn[x],maxx[x]);
		minn[x]=-minn[x];maxx[x]=-maxx[x];
		tag[x]^=1;
	}
	void pushdown(int x){
		if(vis[x]){
			swap(son[x][0],son[x][1]);
			vis[son[x][0]]^=1; vis[son[x][1]]^=1; vis[x]=0;
		}
		if(tag[x]){
			tag[x]=0;
			if(son[x][0]) rever(son[x][0]);
			if(son[x][1]) rever(son[x][1]);
		}
	}
	void rotate(int x){
		int y=f[x],z=f[y],which=get(x);
		if(!isroot(y))  son[z][son[z][1]==y]=x;
		son[y][which]=son[x][which^1]; f[son[y][which]]=y;
		son[x][which^1]=y;  f[y]=x;  f[x]=z;
		updata(y);  updata(x);
	}
	void splay(int x){
		int top(0);  stack[++top]=x;
		for(int i=x;!isroot(i);i=f[i])  stack[++top]=f[i];
		dn(i,top,1)  pushdown(stack[i]);
		for(int y=f[x];!isroot(x);rotate(x),y=f[x])
			if(!isroot(y))  rotate(get(x)==get(y)?y:x);
	}
	void access(int x){for(int t(0);x;t=x,x=f[x])splay(x),son[x][1]=t,updata(x);}
	void reverse(int x){access(x);splay(x);vis[x]^=1;}
	void linkk(int x,int y){reverse(x);f[x]=y;}
	void split(int x,int y){reverse(x);access(y);splay(y);}
}
int main(){
	freopen(FILE".in","r",stdin);
	freopen(FILE".out","w",stdout);
	using namespace Link_Cut_Tree;
	n=read();  cnt=n;
	up(i,0,n) maxx[i]=-INF,minn[i]=INF;
	up(i,1,n-1){
		int x=read()+1,y=read()+1,z=read();
		id[i]=++cnt;  linkk(x,cnt);  linkk(y,cnt);
		v[cnt]=maxx[cnt]=minn[cnt]=sum[cnt]=z;  
	}
	m=read();
	up(i,1,m){
		char ch[5];  scanf("%s",ch);  int x=read(),y=read();
		if(ch[0]=='C'){splay(id[x]);v[id[x]]=y;updata(id[x]);}
		else if(ch[0]=='N'){split(x+1,y+1);rever(y+1);}
		else if(ch[0]=='S'){split(x+1,y+1);printf("%d\n",sum[y+1]);}
		else if(ch[1]=='A'){split(x+1,y+1);printf("%d\n",maxx[y+1]);}
		else {split(x+1,y+1);printf("%d\n",minn[y+1]);}
	}
	return 0;
}