POJ1328

求每个点的圆心的边界值，按从小到大排序之后，

       如果当前最右边的点比下一个点最左边的值大，则ans++;

       如果当前点最右边的值比下一个点最右边的值大，则改变临界值

#include<stdio.h>
#include<math.h>
#include<stdlib.h>
typedef struct
{
    double xl; 
    double xr; 
}coordinate;


int cmp(const void* m,const void* k){
	return ((coordinate*)m)->xl < ((coordinate*)k)->xl?-1:1;
}

int main(){
	int num,x=0,y=0,r,k=0,i,ans,flag;
	coordinate coo[1000]={0};
	double min = 0;
	while(scanf("%d %d",&num,&r),num!=0&&r!=0){
		k++;
		flag = 0;
		for(i=0;i<num;i++){
			scanf("%d %d",&x,&y);
			if(r<y){
				flag=1;
			}
			else {
				coo[i].xl=x-sqrt(r*r-y*y);
				coo[i].xr=x+sqrt(r*r-y*y);
			}
			
		}
		if(flag) {
			printf("Case %d: %d\n",k,-1);
			continue;
		}
		qsort(coo,num,sizeof(coordinate),cmp);
		min = coo[0].xr;
		ans=1;
		for(i=1;i<num;i++){
			if(min < coo[i].xl) {
				ans++;
				min = coo[i].xr;
			}
			else{
				if(coo[i].xr < min )
					min = coo[i].xr;
			}
		}
		printf("Case %d: %d\n",k,ans);
	}
	return 0;
}