POJ 1828 Monkeys' Pride

#include<stdio.h>
#include<algorithm>
using namespace std;
struct Node{
int x;
int y;
}a[50009];
bool cmp(struct Node aa,struct Node bb){
if(aa.y!=bb.y) return aa.y<bb.y;
return aa.x<bb.x;
}
bool Bin_search(int l,int r,int t){
while(l<=r){
int mid=(l+r)/2;
if(a[t].x>a[mid].x){
l=mid+1;
}
if(a[t].x<=a[mid].x) return true;
}
return false;
}
int main(){
int n;
while(~scanf("%d",&n),n){
for(int i=0;i<n;i++){
scanf("%d %d",&a[i].x,&a[i].y);
}
sort(a,a+n,cmp);
int ans=0;
for(int i=0;i<n;i++){
// printf("%d %d %d\n",a[i].x,a[i].y,Bin_search(i+1,n-1,i));
if(Bin_search(i+1,n-1,i)==false){
ans++;
}
}
printf("%d\n",ans);
}
return 0;
}