P3919 【模板】可持久化线段树 1（可持久化数组）

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

源代码

// 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

TLE