POJ 2352 Stars

二维偏序：第一维排序，第二维树状数组或线段树。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define maxn 15050
using namespace std;
struct point
{
    int x,y;
}p[maxn];
int n,hash[maxn],ls[maxn<<2],rs[maxn<<2],val[maxn<<2],root,tot=0,ans[maxn];
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);
}
void pushup(int now)
{
    val[now]=val[ls[now]]+val[rs[now]];
}
void modify(int now,int left,int right,int x)
{
    if ((left==right) && (left==x))
    {
        val[now]++;
        return;
    }
    int mid=(left+right)>>1;
    if (x<=mid) modify(ls[now],left,mid,x);
    else modify(rs[now],mid+1,right,x);
    pushup(now);
}
int ask(int now,int left,int right,int l,int r)
{
    if ((left==l) && (right==r))
        return val[now];
    int mid=(left+right)>>1;
    if (r<=mid) return ask(ls[now],left,mid,l,r);
    else if (l>=mid+1) return ask(rs[now],mid+1,right,l,r);
    else return ask(ls[now],left,mid,l,mid)+ask(rs[now],mid+1,right,mid+1,r);
}
int find(int x)
{
    int left=1,right=n;
    while (left<=right)
    {
        int mid=(left+right)>>1;
        if (hash[mid]==x) return mid;
        else if (hash[mid]<x) left=mid+1;
        else right=mid-1;
    }
}
int main()
{
    scanf("%d",&n);
    for (int i=1;i<=n;i++)
    {
        scanf("%d%d",&p[i].x,&p[i].y);
        hash[i]=p[i].x;
    }
    sort(hash+1,hash+n+1);
    build(root,1,n);
    for (int i=1;i<=n;i++)
    {
        int now=find(p[i].x);
        ans[ask(root,1,n,1,now)]++;
        modify(root,1,n,now);
    }
    for (int i=0;i<=n-1;i++)
        printf("%d
",ans[i]);
    return 0;
}