【POJ】2528 Mayor's posters

#include<cstdio>
#include<cstring>
#include<cstdlib>
#define MAXN 50010
struct node
{
    int x,y;
};
node a[MAXN],p[MAXN];
int cmp(const void *a,const void *b)
{
    return (*(node *)a).x-(*(node *)b).x;
}
int ans,tree[MAXN<<2];
bool vis[MAXN];
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(mid>=x)
            Update(x,y,val,L,mid,rt<<1);
        if(y>mid)
            Update(x,y,val,mid+1,R,rt<<1|1);
    }
}
void Query(int L,int R,int rt)
{
    if(tree[rt])
    {
        if(!vis[tree[rt]])
        {
            vis[tree[rt]]=true;
            ans++;
        }
    }
    else if(L!=R)
    {
        int mid=(L+R)>>1;
        Query(L,mid,rt<<1);
        Query(mid+1,R,rt<<1|1);
    }
}
int Bin(int low,int high,int val)
{
    int mid;
    while(low<high)
    {
        mid=(high+low)>>1;
        if(a[mid].x==val)
            return a[mid].y;
        if(a[mid].x>val)
            high=mid;
        else
            low=mid+1;
    }
}
int main()
{
    int c,n,i,j,k;
    scanf("%d",&c);
    while(c--)
    {
        scanf("%d",&n);
        for(i=k=0;i<n;i++)
        {
            scanf("%d%d",&p[i].x,&p[i].y);
            a[k++].x=p[i].x;
            a[k++].x=p[i].y;
        }
        qsort(a,k,sizeof(a[0]),cmp);
        for(i=j=0;i<k;i++)
        {
            if(a[i].x!=a[j].x)
                a[++j]=a[i];
        }
        k=j+1;
        a[0].y=j=1;
        for(i=1;i<k;i++)
        {
            if(a[i].x==a[i-1].x+1)
                j++;
            else
                j+=2;
            a[i].y=j;
        }
        memset(tree,0,sizeof(tree));
        memset(vis,false,sizeof(vis));
        for(i=ans=0;i<n;i++)
            Update(Bin(0,k,p[i].x),Bin(0,k,p[i].y),i+1,1,j,1);
        Query(1,j,1);
        printf("%d\n",ans);
    }
    return 0;
}