主席树6分求助

#include<bits/stdc++.h>

using namespace std;

const int MX=21*1000000+10;
#define LL long long
#define inf 0x7fffffff

struct tk
{
	int l,r;
	int value;
}tree[MX];
int top=0;
int root[MX];

int n,m;
int w[MX];

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-48;ch=getchar();}
    return x*f;
}

inline int create(int node)
{
	tree[++top]=tree[node];
	return top;
}

inline int build(int now,int l,int r)
{
	top++;
	now=top;
	if(l==r)
	{
		tree[now].value=w[l];
		return top;
	}
	int mid=(l+r)>>1;
	tree[now].l=build(tree[now].l,l,mid);
	tree[now].r=build(tree[now].r,mid+1,r);
	return now;
}

inline int updata(int now,int l,int r,int x,int nval)
{
	now=create(now);
	if(l==r)
	{
		tree[now].value=nval;
	}
	else
	{	
		int mid=(l+r)>>1;
		if(x<=mid)
		{
			tree[now].l=updata(tree[now].l,l,mid,x,nval);
		}
		else
		{
			tree[now].l=updata(tree[now].r,mid+1,r,x,nval);
		}
	}
	return now;
}

inline int query(int now,int l,int r,int x)
{
	if(l==r)
	{
		return tree[now].value;
	}
	else
	{
		int mid=(l+r)>>1;
		if(x<=mid) return query(tree[now].l,l,mid,x);
		else return query(tree[now].r,mid+1,r,x);
	}
}

int main()
{
	//freopen("1.in","r",stdin);
	//freopen("1.out","w",stdout);
	n=read(),m=read();
	for(int i=1;i<=n;i++)
	{
		w[i]=read();
	}
	root[0]=build(0,1,n);
	for(int i=1;i<=m;i++)
	{
		int v1,cz,loc;
		v1=read(),cz=read(),loc=read();
		if(cz==1)
		{
			int nval;
			nval=read();
			root[i]=updata(root[v1],1,n,loc,nval);
		}
		else if(cz==2)
		{
			printf("%d\n", query(root[v1],1,n,loc)); 
			root[i]=root[v1];
		}
	}
	return 0;
}