CF1000F One Occurrence 主席树 线段树

#include<bits/stdc++.h>
using namespace std;
#define ll long long
const int N=5e5+10;
struct node{int minn,num;}t[N<<6];
node merge(node a,node b)
{
    if(a.minn<b.minn)return (node){a.minn,a.num};
    else return (node){b.minn,b.num};
}
int lson[N<<6],rson[N<<6],n,m,last[N],pos[N],a[N],T[N],ncnt;
void build(int l,int r,int &pos)
{
    pos=++ncnt;
    if(l==r){t[pos]=(node){1000000000,0};return ;}
    int m=(l+r)>>1;
    build(l,m,lson[pos]);build(m+1,r,rson[pos]);
    t[pos]=merge(t[lson[pos]],t[rson[pos]]);
}
void upnode(int x,int v,int num,int l,int r,int pre,int &pos)
{
    pos=++ncnt;
    lson[pos]=lson[pre];
    rson[pos]=rson[pre];
    t[pos]=t[pre];
    if(l==r){t[pos]=(node){v,num};return ;}
    int m=(l+r)>>1;
    if(x<=m)upnode(x,v,num,l,m,lson[pre],lson[pos]);
    else upnode(x,v,num,m+1,r,rson[pre],rson[pos]);
    t[pos]=merge(t[lson[pos]],t[rson[pos]]);
}
node qmin(int L,int R,int l,int r,int pos)
{
    if(L<=l&&r<=R)return t[pos];
    node ans=(node){100000000,0};
    int m=(l+r)>>1;
    if(L<=m)ans=merge(ans,qmin(L,R,l,m,lson[pos]));
    if(R>m) ans=merge(ans,qmin(L,R,m+1,r,rson[pos]));
    return ans;
}
int main()
{
    cin>>n;node ans;
    for(int i=1;i<=n;i++)scanf("%d",&a[i]);
    for(int i=1;i<=n;i++)
    {
        last[i]=pos[a[i]];
        pos[a[i]]=i;
    }
    build(1,n,T[0]);
    for(int i=1;i<=n;i++)
    {    
        T[i]=T[i-1];
        upnode(i,last[i],a[i],1,n,T[i],T[i]);
        if(last[i])    
        {
            upnode(last[i],100000000,0,1,n,T[i],T[i]);
        }
    }
    cin>>m;int l,r;
    while(m--)
    {
        scanf("%d%d",&l,&r);
        ans=qmin(l,r,1,n,T[r]);
        if(ans.minn<l)printf("%d\n",ans.num);
        else printf("0\n");
    }
    return 0;
}