2017ecjtu-summer training #5 UVA10382

#include<iostream>
#include<stdio.h>
#include<string.h>
#include<cmath>
#include<algorithm>
#define maxn 10010
using namespace std;
struct node
{
    double left;
    double right;
} a[maxn];
bool cmp(node a,node b)
{
    return a.left<b.left;
}
int n;
double l,w;
int main()
{
    int i,j,k;
    while(scanf("%d %lf %lf",&n,&l,&w)!=EOF)
    {
        int len=0;
        double p,r;
        for(i=0; i<n; i++)
        {
            scanf("%lf%lf",&p,&r);
            if(2*r<=w)
                continue;
            double k=sqrt(r*r-w*w/4.0);
            a[len].right=p+k;
            a[len].left=p-k;
            len++;
        }
        sort(a,a+len,cmp);
        int sum=0;
        double le=0,ri=0;
        int flag=0;
        if(a[0].left<=0)
        {
            int i=0;
            while(i<len)
            {
                int j=i;
                while(le>=a[j].left&&j<len)
                {
                    if(a[j].right>ri)
                        ri=a[j].right;
                    j++;
                }
                if(i==j)
                    break;
                sum++;
                le=ri;
                i=j;
                if(ri>=l)
                {
                    flag=1;
                    break;
                }
            }
        }
        if(flag)
            printf("%d\n",sum);
        else
            printf("-1\n");
    }
    return 0;
}