【主席树】【模板】

刚学主席树，理解还不是很深，先粘一下板子吧。

模板1

Code

#include<bits/stdc++.h>
using namespace std;

inline int read()
{
	register int x=0,w=1;
	register char ch=getchar();
	while((ch<'0'||ch>'9')&&ch!='-') ch=getchar();
	if(ch=='-') {w=-1;ch=getchar();}
	while(ch>='0'&&ch<='9') {x=(x<<3)+(x<<1)+(ch^48);ch=getchar();}
	return x*w;
}
inline void write(int x)
{
	if(x<0){x=~(x-1);putchar('-');}
	if(x>9) write(x/10);
	putchar(x%10+'0'); 
}
const int N=1e6+10;
int rt[N];
struct node{
	int ls,rs,val;
}t[N*25];
int n,m,a[N];
int tot;
int build(int l,int r)
{
	int p=++tot;
	if(l==r){
		t[p].val=a[l];
		return p;
	}
	int mid=l+r>>1;
	t[p].ls=build(l,mid);
	t[p].rs=build(mid+1,r);
	return p;
}
int insert(int now,int l,int r,int pos,int val)
{
	int p=++tot;
	t[p]=t[now];
	if(l==r){
		t[p].val=val;
		return p;
	}
	int mid=l+r>>1;
	if(pos<=mid) t[p].ls=insert(t[now].ls,l,mid,pos,val);
	else t[p].rs=insert(t[now].rs,mid+1,r,pos,val);
	return p;
}
int query(int x,int l,int r,int pos)
{
	if(l==r) return t[x].val;
	int mid=l+r>>1;
	if(pos<=mid) return query(t[x].ls,l,mid,pos);
	return query(t[x].rs,mid+1,r,pos);
}
int main()
{
    n=read();m=read();
    for(int i=1;i<=n;++i) a[i]=read();
    rt[0]=build(1,n);
    for(int i=1;i<=m;++i)
    {
    	int r=read(),o=read(),pos=read();
    	if(o==1){
    		int val=read();
    		rt[i]=insert(rt[r],1,n,pos,val);
		}
		else{
		write(query(rt[r],1,n,pos));puts(""); 
		rt[i]=rt[r];
		}
	}
	return 0;
}

模板2（静态区间第k小）

#include<bits/stdc++.h>
using namespace std;

inline int read()
{
	register int x=0,w=1;
	register char ch=getchar();
	while((ch<'0'||ch>'9')&&ch!='-') ch=getchar();
	if(ch=='-') {w=-1;ch=getchar();}
	while(ch>='0'&&ch<='9') {x=(x<<3)+(x<<1)+(ch^48);ch=getchar();}
	return x*w;
}
const int N=2e5+100;
int n,m,a[N],rk[N];
int rt[N],tot;
struct node{
	int ls,rs,sum;
}t[N*40];
int build(int l,int r)
{
	int p=++tot;
	if(l==r) return p;
	int mid=l+r>>1;
	t[p].ls=build(l,mid);
	t[p].rs=build(mid+1,r);
	return p;
}
void pushup(int x)
{
	t[x].sum=t[t[x].ls].sum+t[t[x].rs].sum;
}
int insert(int x,int l,int r,int pos)
{
	int p=++tot;
	t[p]=t[x];
	if(l==r){
		t[p].sum++;
		return p;
	}
	int mid=l+r>>1;
	if(pos<=mid) t[p].ls=insert(t[p].ls,l,mid,pos);
	else t[p].rs=insert(t[p].rs,mid+1,r,pos);
	pushup(p);
	return p;
}
inline void write(int x)
{
	if(x<0) {putchar('-');x=~(x-1);}
	if(x>9) write(x/10);
	putchar(x%10+'0');
}
int query(int p,int q,int l,int r,int k)
{
	if(l==r) return rk[l];
	int mid=l+r>>1;
	int lsum=t[t[q].ls].sum-t[t[p].ls].sum;
	if(k<=lsum) return query(t[p].ls,t[q].ls,l,mid,k);
	return query(t[p].rs,t[q].rs,mid+1,r,k-lsum);
}
int main()
{
    n=read();m=read();
    for(int i=1;i<=n;++i){
    	a[i]=rk[i]=read();
	}
	sort(rk+1,rk+n+1);
	int cnt=unique(rk+1,rk+n+1)-rk-1;
	for(int i=1;i<=n;++i){
		a[i]=lower_bound(rk+1,rk+cnt+1,a[i])-rk;
	}
	rt[0]=build(1,cnt);
	for(int i=1;i<=n;++i){
		rt[i]=insert(rt[i-1],1,cnt,a[i]);
	}
	for(int i=1;i<=m;++i)
	{
		int l=read(),r=read(),k=read();
		write(query(rt[l-1],rt[r],1,cnt,k));puts("");
	}
	return 0;
}