10382 - Watering Grass uva贪心

#include<cstdio>
#include<iostream>
#include<cstring>
#include<algorithm>
#include<cmath>
using namespace std;
#define MAX_SIZE 10000 + 100
struct Circle
{
    double x;
    double y;
    friend bool operator <(const Circle & a,const Circle & b){
       return a.x<b.x;
   }
};
int main()
{
    int n,l,w;
    while(scanf("%d%d%d",&n,&l,&w)!=EOF){
        int m=0;
        Circle cir[MAX_SIZE];
        for(int i=0;i<n;i++){
            double o,r;
            scanf("%lf%lf",&o,&r);
            if(r>=1.0*w/2){
                cir[m].x=o-sqrt(r*r-1.0*w*w/4);
                cir[m].y=o+sqrt(r*r-1.0*w*w/4);
                m++;
            }
        }
        sort(cir,cir+m);
        int ok=0;
        double next=0;
        double maxs=-9999;
        int can=1;
        int counts=0;
        for(int i=0;i<m;i++){
            if(cir[i].x<=next){
                ok=1;
                if(cir[i].y>maxs){
                    maxs=cir[i].y;
                }
            }
            else if(cir[i].x>next&&ok==1){
                next=maxs;
                maxs=-99999;
                counts++;
                ok=0;
                i--;
            }
            else if(cir[i].x>next&&ok==0)
            {
                can=0;
                break;
            }
        }
        if(ok==1){
            next=maxs;
            counts++;
        }
        if(!can) printf("-1");
        else if(next>=l) printf("%d",counts);
        else if(next<l)  printf("-1");
        printf("\n");
    }
    return 0;
}