Weight [tree line]

A simple template question;

Also remember remember it, so my mind was not very good and forget.

Luo Valley 1168

#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstring>
#include<algorithm>
using namespace std;
const int N=1e5+5;
int n;
int a[N],b[N];
struct Tree
{
int l,r,mid;
int num;
}tree[N<<2];
int read()
{
char c=getchar();int num=0;
for(;!isdigit(c);c=getchar());
for(;isdigit(c);c=getchar())
num=num*10+c-'0';
return num;
}
void build(int root,int l,int r)
{
tree[root].l=l,tree[root].r=r,tree[root].mid=l+r>>1;
if(l==r)
return;
build(root<<1,l,tree[root].mid);
build(root<<1|1,tree[root].mid+1,r);
}
void update(int root,int x)
{
++tree[root].num;
if(tree[root].l==tree[root].r)
return;
if(x<=tree[root].mid)
update(root<<1,x);
else
update(root<<1|1,x);
}
int query(int root,int num)
{
if(tree[root].l==tree[root].r)
return tree[root].l;
if(num<=tree[root<<1].num)
return(query(root<<1,num));
else
return(query(root<<1|1,num-tree[root<<1].num));
}
int main()
{
n=read();
for(int i=1;i<=n;++i)
a[i]=read(),b[i]=a[i];
sort(b+1,b+n+1);
int bound=unique(b+1,b+n+1)-b;
build(1,1,n);
for(int i=1;i<=n;++i){
int pos=lower_bound(b+1,b+bound+1,a[i])-b;
update(1,pos);
if(i%2)
printf("%d\n",b[query(1,i/2+1)]);
}
return 0;
}