AC日记——中庸之道 codevs 2021

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>

using namespace std;

struct TreeNodeType {
    int l,r,dis;
    
    TreeNodeType *left,*right;
};
struct TreeNodeType *root[1001];

int n,q,if_z,num[1001],num_[1001],size;

char Cget;

inline void read_int(int &now)
{
    now=0,if_z=1,Cget=getchar();
    while(Cget>‘9‘||Cget<‘0‘)
    {
        if(Cget==‘-‘) if_z=-1;
        Cget=getchar();
    }
    while(Cget>=‘0‘&&Cget<=‘9‘)
    {
        now=now*10+Cget-‘0‘;
        Cget=getchar();
    }
    now*=if_z;
}

void tree_build(TreeNodeType *&now,int l,int r)
{
    now=new TreeNodeType;
    now->l=l,now->r=r,now->dis=0;
    if(l==r) return ;
    int mid=(l+r)>>1;
    tree_build(now->left,l,mid);
    tree_build(now->right,mid+1,r);
}

void tree_change(TreeNodeType *&pre,int to,TreeNodeType *&now)
{
    now=new TreeNodeType;
    now->l=pre->l,now->r=pre->r,now->dis=pre->dis+1;
    if(now->l==now->r) return ;
    int mid=(now->l+now->r)>>1;
    if(to<=mid)
    {
        now->right=pre->right;
        tree_change(pre->left,to,now->left);
    }
    else
    {
        now->left=pre->left;
        tree_change(pre->right,to,now->right);
    }
}

int tree_query(TreeNodeType *pre,TreeNodeType *now,int to)
{
    if(now->l==now->r) return now->l;
    int dis=now->left->dis-pre->left->dis;
    if(to<=dis) return tree_query(pre->left,now->left,to);
    else return tree_query(pre->right,now->right,to-dis); 
}

int main()
{
    read_int(n),read_int(q);
    for(int i=1;i<=n;i++)
    {
        read_int(num[i]);
        num_[i]=num[i];
    }
    sort(num+1,num+n+1);
    size=unique(num+1,num+n+1)-num-1;
    tree_build(root[0],1,size);
    for(int i=1;i<=n;i++)
    {
        num_[i]=lower_bound(num+1,num+size+1,num_[i])-num;
        tree_change(root[i-1],num_[i],root[i]);
    }
    int l,r;
    for(int i=1;i<=q;i++)
    {
        read_int(l),read_int(r);
        int mid=((r-l+1)>>1)+1;
        printf("%d\n",num[tree_query(root[l-1],root[r],mid)]);
    }
    return 0;
}