【POJ】1436 Horizontally Visible Segments

#include<cstdio>
#include<cstring>
#include<vector>
#include<algorithm>
#include<set>
using namespace std;
#define MAXN 16010
#define INF 123456789
struct Seg
{
    int y1,y2,x;
    friend bool operator<(Seg a,Seg b)
    {
        return a.x<b.x;
    }
};
int i,tree[MAXN<<2];
Seg p[MAXN];
vector<int>G[MAXN];
vector<int>::iterator it;
inline void PushDown(int rt)
{
    if(tree[rt])
    {
        tree[rt<<1]=tree[rt<<1|1]=tree[rt];
        tree[rt]=0;
    }
}
void Update(int x,int y,int val,int L,int R,int rt)
{
    if(x<=L&&R<=y)
        tree[rt]=val;
    else
    {
        int mid=(L+R)>>1;
        PushDown(rt);
        if(x<=mid)
            Update(x,y,val,L,mid,rt<<1);
        if(y>mid)
            Update(x,y,val,mid+1,R,rt<<1|1);
    }
}
void Query(int x,int y,int L,int R,int rt)
{
    if(x<=L&&R<=y)
    {
        if(tree[rt])
        {
            G[i].push_back(tree[rt]);
            G[tree[rt]].push_back(i);
        }
        else if(L!=R)
        {
            int mid=(L+R)>>1;
            Query(x,y,L,mid,rt<<1);
            Query(x,y,mid+1,R,rt<<1|1);
        }
    }
    else
    {
        int mid=(L+R)>>1;
        PushDown(rt);
        if(x<=mid)
            Query(x,y,L,mid,rt<<1);
        if(y>mid)
            Query(x,y,mid+1,R,rt<<1|1);
    }
}
int main()
{
    int t,n,j,k,r,left,right,ans;
    scanf("%d",&t);
    while(t--)
    {
        left=INF;
        ans=right=0;
        scanf("%d",&n);
        for(i=1;i<=n;i++)
        {
            scanf("%d%d%d",&p[i].y1,&p[i].y2,&p[i].x);
            p[i].y1<<=1;
            p[i].y2<<=1;
            left=min(left,p[i].y1);
            right=max(right,p[i].y2);
            G[i].clear();
        }
        sort(p+1,p+1+n);
        memset(tree,0,sizeof(tree));
        for(i=1;i<=n;i++)
        {
            Query(p[i].y1,p[i].y2,left,right,1);
            Update(p[i].y1,p[i].y2,i,left,right,1);
        }
        for(i=1;i<=n;i++)
        {
            sort(G[i].begin(),G[i].end());
            it=unique(G[i].begin(),G[i].end());
            G[i].resize(it-G[i].begin());
        }
        for(i=1;i<=n;i++)
        {
            for(j=0;j<G[i].size();j++)
            {
                for(k=j+1;k<G[i].size();k++)
                {
                    r=lower_bound(G[G[i][j]].begin(),G[G[i][j]].end(),G[i][k])-G[G[i][j]].begin();
                    if(r<G[G[i][j]].size()&&G[G[i][j]][r]==G[i][k])
                        ans++;
                }
            }
        }
        printf("%d\n",ans/3);
    }
    return 0;
}