P3919 【模板】可持久化线段树 1（可持久化数组） · znzryb
## 思路讲解
其实不难，理解之后写起来还是挺简单的。
先是小T了一下，然后上了读写优化就好了。
## AC代码
[https://www.luogu.com.cn/record/218184451](https://www.luogu.com.cn/record/218184451)
::: 源代码
```cpp
// Problem: P3919 【模板】可持久化线段树 1（可持久化数组）
// Contest: Luogu
// URL: https://www.luogu.com.cn/problem/P3919
// Memory Limit: 1 MB
// Time Limit: 1500 ms
// by znzryb
//
// Powered by CP Editor (https://cpeditor.org)
#include <bits/stdc++.h>
#define all(vec) vec.begin(),vec.end()
#define CLR(i,a) memset(i,a,sizeof(i))
#define fi first
#define se second
#define pb push_back
#define SZ(a) ((int) a.size())
#define FOR(i, a, b) for (int i = (a); i <= (b); ++i)
#define ROF(i, a, b) for (int i = (a); i >= (b); --i)
#define getFro(vec) (vec.empty()?0:vec.front())
#define getBac(vec) (vec.empty()?0:vec.front())
#define debug(var) cerr << #var <<":"<<var<<"\n";
#define DEBUG(variable) \
do { \
std::cerr << #variable << ":"; \
for (const auto& elem : variable) { \
std::cerr << elem << " "; \
} \
std::cerr << "\n"; \
} while (0)
#define uniVec(var) \
do { \
sort(var.begin(),var.end());\
var.resize(unique(var.begin(),var.end())-var.begin());\
} while (0)
#define debugN(var,N) \
do{ \
std::cerr<<#var<<":"; \
FOR(i,1,N){ \
std::cerr<<var[i]<<" "; \
} \
std::cerr<<"\n"; \
}while(0)
#define debugMap(variable) \
do { \
std::cerr << #variable << ":\n"; \
for (const auto& pair : variable) { \
std::cerr << " " << pair.first << " => " << pair.second << "\n"; \
} \
std::cerr << std::endl; \
} while (0)
#define lson(var) (var<<1)
#define rson(var) ((var<<1)+1)
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef __int128 i128;
typedef pair<ll,ll> pll;
typedef array<ll,3> arr3;
typedef array<ll,2> arr2;
typedef double DB;
typedef long double LD;
typedef pair<DB,DB> pdd;
typedef pair<ll,bool> plb;
constexpr ll MAXN=static_cast<ll>(1e6)+10,INF=static_cast<ll>(1e18)+3;
constexpr ll mod=static_cast<ll>(1e9)+7;
constexpr double eps=1e-8;
ll N,M,Q,X,K,T,A[MAXN];
/*
*/
struct zhuXiTree{ // 主席树单点修改
ll Cver=0;
struct Tree{
ll lson,rson,val,l,r;
};
ll idx=1;
vector<Tree> tr;vector<ll> verN,org;
zhuXiTree(ll n,ll m){ // n为数组长度，m为查询次数
ll ln=n*4+m*ceil(log2(n))+131;
tr.resize(ln);
verN.resize(m+5);
org.resize(n+5);
verN[Cver]=idx;
}
void buildTree(ll node,ll l,ll r){
if(l==r){
tr[node].val=org[l];
tr[node].l=l;
tr[node].r=r;
return;
}
tr[node].l=l;
tr[node].r=r;
tr[node].lson=++idx;
tr[node].rson=++idx;
buildTree(tr[node].lson,l,(l+r)>>1);
buildTree(tr[node].rson,((l+r)>>1)+1,r);
}
void modify(ll node,ll ver,ll pos,ll x){
tr[++idx].lson=tr[node].lson;
tr[idx].rson=tr[node].rson;
tr[idx].val=tr[node].val;
tr[idx].l=tr[node].l;
tr[idx].r=tr[node].r;
if(verN[ver]==node){
++Cver;
verN[Cver]=idx;
}
if(tr[idx].l==tr[idx].r){
if(tr[idx].l==pos) tr[idx].val=x;
return;
}
ll mid=tr[idx].l+tr[idx].r>>1;
if(pos<=mid){
tr[idx].lson=idx+1;
modify(tr[node].lson,ver,pos,x);
}else{
tr[idx].rson=idx+1;
modify(tr[node].rson,ver,pos,x);
}
}
ll query(ll node,ll ver,ll pos){
tr[++idx].lson=tr[node].lson;
tr[idx].rson=tr[node].rson;
tr[idx].val=tr[node].val;
tr[idx].l=tr[node].l;
tr[idx].r=tr[node].r;
if(verN[ver]==node){
++Cver;
verN[Cver]=idx;
}
if(tr[idx].l==tr[idx].r){
return tr[idx].val;
}
ll mid=tr[idx].l+tr[idx].r>>1;
if(pos<=mid){
tr[idx].lson=idx+1;
return query(tr[node].lson,ver,pos);
}else{
tr[idx].rson=idx+1;
return query(tr[node].rson,ver,pos);
}
}
};
inline ll read()
{
ll 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-'0',ch=getchar();
return x*f;
}
inline void solve(){
N=read();
M=read();
zhuXiTree tr(N,M);
FOR(i,1,N){
tr.org[i]=read();
}
tr.buildTree(1,1,N);
FOR(i,1,M){
ll ver=read(),op=read(),pos=read(),x;
if(op==1){
x=read();
tr.modify(tr.verN[ver],ver,pos,x);
}else{
ll ans=tr.query(tr.verN[ver],ver,pos);
cout<<ans<<"\n";
}
}
}
int main()
{
ios::sync_with_stdio(false);
cin.tie(0);cout.tie(0);
// cin>>T;
// while(T--){
// solve();
// }
solve();
return 0;
}
/*
TLE https://www.luogu.com.cn/record/218183673 TLE了一个点
AC https://www.luogu.com.cn/record/218184451
*/
```
:::
## 心路历程（WA，TLE，MLE……）
[https://www.luogu.com.cn/record/218183673](https://www.luogu.com.cn/record/218183673)
TLE