> I don't know why I always get WA. Someone plzzz help me!
> 
> #include <iostream>
> #include <math.h>
> #include <stdio.h>
> #include <stdlib.h>
> using namespace std;
> 
> typedef struct{
>   double left;
>   double right;
> }INTERVAL;
> 
> int compare(const void* a, const void* b){
>   INTERVAL* i1= (INTERVAL*) a;
>   INTERVAL* i2= (INTERVAL*) b;
>   return (*i1).left-(*i2).left;
> }
> 
> int main(){
>   int x,y,r;
>   int numCase;
>   double x0,r0;
>   bool error=false;
>   int i,t,caseNow;
>   INTERVAL interval[1001];
>   int size=0;
>   int result;
>   caseNow=0;
>   while (1){
>     size=0;
>     result=1;
>     caseNow++;
>     error=false;
>     cin >>numCase>>r;
>     if (!numCase && !r) return 0;
>     if(r<=0) error=true;
>     for (i=0;i<numCase;i++){
>       cin >>x>>y;
>       r0=sqrt(r*r-y*y);
>       if(r<y) error=true;
>       if(y<0) error=true;
>       r0=x-r0;
>       interval[i].left=r0-r;
>       interval[i].right=r0+r;
>       //cout <<interval[i].left<<"  "<<interval[i].right<<endl;
> 
>       size++;
>    }
>    if(error){
>      cout <<"Case "<<caseNow<<": -1"<<endl;
>    }else{
>      qsort(interval,numCase,sizeof(INTERVAL),compare);
>      //for (i=0;i<numCase;i++)        cout <<interval[i].left<<"  "<<interval[i].right<<endl;
>      for(i=1; i<numCase;i++){
>      //  cout <<"result"<<result<<endl;
>      //  cout <<interval[i].left<<"  "<<interval[i-1].right<<endl;
>      //  cout <<((interval[i].left) > (interval[i-1].right))<<endl;
>        if ((interval[i].left) > (interval[i-1].right)) result++;
>      }
>     cout <<"Case "<<caseNow<<": "<<result<<endl;
>   }
>   }
>   return 0;
> }
I think  y can <0