POJ 2528 Mayor's posters

#include<iostream>
#include<cstring>
#include<cstdio>
#include<algorithm>
#define maxn 50500
using namespace std;
int t,n,tot=0,root,x[maxn],y[maxn],ans=0,hash[maxn],cnt=0,len=0;
bool vis[maxn];
int ls[maxn<<2],rs[maxn<<2],lazy[maxn<<2];
void build(int &now,int left,int right)
{
    now=++tot;
    if (left==right) return;
    int mid=(left+right)>>1;
    build(ls[now],left,mid);
    build(rs[now],mid+1,right);
    return;
}
void modify(int now,int left,int right,int l,int r,int x)
{
    if ((left==l) && (right==r))
    {
        lazy[now]=max(lazy[now],x);
        return;
    }
    int mid=(left+right)>>1;
    if (r<=mid) modify(ls[now],left,mid,l,r,x);
    else if (l>=mid+1) modify(rs[now],mid+1,right,l,r,x);
    else
    {
        modify(ls[now],left,mid,l,mid,x);
        modify(rs[now],mid+1,right,mid+1,r,x);
    }
    return;
}
int ask(int now,int left,int right,int pos)
{
    if ((left==right) && (left==pos))
        return lazy[now];
    int mid=(left+right)>>1;
    if (pos<=mid) return max(ask(ls[now],left,mid,pos),lazy[now]);
    else return max(ask(rs[now],mid+1,right,pos),lazy[now]);
}
void work()
{
    memset(vis,false,sizeof(vis));
    memset(lazy,0,sizeof(lazy));
    cnt=0;tot=0;len=0;ans=0;
    scanf("%d",&n);
    for (int i=1;i<=n;i++)
    {
        scanf("%d%d",&x[i],&y[i]);
        hash[++cnt]=x[i];hash[++cnt]=y[i];
    }
    sort(hash+1,hash+cnt+1);
    len=unique(hash+1,hash+cnt+1)-hash-1;
    build(root,1,len);
    for (int i=1;i<=n;i++)
    {
        int l=lower_bound(hash+1,hash+len+1,x[i])-hash;
        int r=lower_bound(hash+1,hash+len+1,y[i])-hash;
        modify(root,1,len,l,r,i);
    }
    for (int i=1;i<=len;i++)
        vis[ask(root,1,len,i)]=true;
    for (int i=1;i<=n;i++)
        if (vis[i])
            ans++;
    printf("%d\n",ans);
}
int main()
{
    scanf("%d",&t);
    for (int i=1;i<=t;i++)
        work();
    return 0;
}