【模板】可持久化线段树

#include <bits/stdc++.h>
using namespace std;
 
const int maxN = 1e6+10;
 
int roots[maxN*30];
int cnt;
int A[maxN];
 
struct Tree{
	struct Node{
		int val;
		int lson;
		int rson;
		Node(int val=0,int lson=0,int rson=0):val(val),lson(lson),rson(rson){};
	}node[maxN*30];
	
	void build(int &root,int l,int r){
		root = ++cnt;
		if(l == r){
			node[root].val = A[l];
			return;
		}
		int mid = (l + r) >> 1;
		build(node[root].lson,l,mid);
		build(node[root].rson,mid+1,r);
	}
	
	inline int clone(int k){
		node[++cnt] = node[k];
		return cnt;
	}
	
	int update(int root,int l,int r,int x,int val){
		root = clone(root);
		if(l == r){
			node[root].val = val;
		}else{
			int mid = (l + r) >> 1;
			if(x <= mid){
				node[root].lson = update(node[root].lson,l,mid,x,val);
			}else{
				node[root].rson = update(node[root].rson,mid+1,r,x,val);
			}
		}
		return root;
	}
	
	int Query(int root,int l,int r,int x){
		if(l == r) return node[root].val;
		int mid = (l + r) >> 1;
		if(x <= mid) return Query(node[root].lson,l,mid,x);
		else return Query(node[root].rson,mid+1,r,x);
	}
}SegmentTree;
 
int main(){
	int N,M;
	scanf("%d%d",&N,&M);
	for(int i = 1;i<=N;i++) scanf("%d",&A[i]);
	SegmentTree.build(roots[0],1,N);
	for(int i = 1;i<=M;i++){
		int v,opt,loc,val;
		scanf("%d%d%d",&v,&opt,&loc);
		if(opt & 1){
			scanf("%d",&val);
			roots[i] = SegmentTree.update(roots[v],1,N,loc,val);
		}else{
			int ans = SegmentTree.Query(roots[v],1,N,loc);
			printf("%d\n",ans);
			roots[i] = roots[v];
		}
	}
	return 0;
}