帮 @xsyyds 求助 LCT 卡常。

#include<iostream>
#include<algorithm>
#include<cstring>
#include<cstdio>
using namespace std;
const int N=1e6+10;
int fa[N],tree[N][2];
bool lazy[N];
long long maxx[N],val[N],lazy1[N],lazy2[N];
inline int read(){
	int x=0,f=1;char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-') f=-1;ch=getchar();}
	while(ch>='0'&&ch<='9'){x=x*10+ch-48;ch=getchar();}
	return x*f;
}
bool nroot(int x){
	return tree[fa[x]][1]==x^tree[fa[x]][0]==x;
}
void pushup(int x){
	maxx[x]=val[x];
	if(tree[x][1])maxx[x]=max(maxx[x],maxx[tree[x][1]]);
	if(tree[x][0])maxx[x]=max(maxx[x],maxx[tree[x][0]]);
}
void pushdown(int x){
	if(lazy[x]){
		swap(tree[x][0],tree[x][1]);
		lazy[tree[x][1]]^=1;
		lazy[tree[x][0]]^=1;
		lazy[x]=0;
	}   	
	if(lazy1[x]!=-1e15){
		if(tree[x][1])val[tree[x][1]]=lazy1[x],maxx[tree[x][1]]=lazy1[x];
		if(tree[x][0])val[tree[x][0]]=lazy1[x],maxx[tree[x][0]]=lazy1[x];
		lazy1[tree[x][1]]=lazy1[tree[x][0]]=lazy1[x];
		lazy2[tree[x][1]]=lazy2[tree[x][0]]=0;
		lazy1[x]=-1e15;
	}
	if(lazy2[x]){
		if(tree[x][1])val[tree[x][1]]+=lazy2[x],maxx[tree[x][1]]+=lazy2[x];
		if(tree[x][0])val[tree[x][0]]+=lazy2[x],maxx[tree[x][0]]+=lazy2[x];
		lazy2[tree[x][1]]+=lazy2[x];
		lazy2[tree[x][0]]+=lazy2[x];
		lazy2[x]=0;
	}
}
void pushall(int x){
	if(nroot(x))pushall(fa[x]);
	pushdown(x);
}
void rotate(int x){
	int y=fa[x],z=fa[y],k=tree[y][1]==x,w=tree[x][!k];
	if(nroot(y))tree[z][tree[z][1]==y]=x;tree[x][!k]=y,tree[y][k]=w;
	if(w)fa[w]=y;fa[y]=x,fa[x]=z;
	pushup(y);
}
void splay(int x){
	pushall(x);
	while(nroot(x)){
		int y=fa[x],z=fa[y];
		if(nroot(y))rotate(tree[y][0]==x^tree[z][0]==y?x:y);
		rotate(x);
	}
	pushup(x);
}
void access(int x){
	for(int y=0;x;x=fa[y=x])
		splay(x),tree[x][1]=y,pushup(x);
}
inline void makeroot(int x){
	access(x);
	splay(x);
	lazy[x]^=1;
}
inline void split(int x,int y){
	makeroot(x);
	access(y);
	splay(y);
}
signed main(){
	int n(read()),m(read());
	for(int i=1;i<=n;++i){
		maxx[i]=val[i]=read();
		lazy[i]=-1e15;
		if(i==1)continue;
		fa[i-1]=i;
	}
	for(int i=1;i<=m;++i){
		int tt(read()),a(read()),b(read());
		if(tt==1){
			int c(read());
			split(a,b);
			lazy2[b]=0;
			lazy1[b]=c;
			maxx[b]=c;
			val[b]=c;
		}
		else if(tt==2){
			int c(read());
			split(a,b);
			lazy2[b]+=c;
			maxx[b]+=c;
			val[b]+=c;
		}
		else{
			split(a,b);
			printf("%lld\n",maxx[b]);
		}
	}
	return 0;
}