UVA 10382 Watering Grass

#include<stdio.h>
#include<string.h>
#include<math.h>
#include<algorithm>
#define MAXN 10010
const double eps = 1e-10;
int N, M;
double L, W;
struct Seg
{
double x, y;
bool operator < (const Seg &t) const
{
return x < t.x;
}
}seg[MAXN];
int dcmp(double x)
{
return (x > eps) - (x < -eps);
}
double sqr(double x)
{
return x * x;
}
void input()
{
M = 0;
for(int i = 0; i < N; i ++)
{
double p, r;
scanf("%lf%lf", &p, &r);
if(dcmp(2 * r - W) <= 0) continue;
double l = sqrt(sqr(r) - sqr(W * 0.5));
seg[M].x = p - l, seg[M].y = p + l, ++ M;
}
std::sort(seg, seg + M);
}
int process()
{
int cnt = 0;
double x = 0, y = 0;
for(int i = 0; i < M; i ++)
{
if(dcmp(seg[i].x - x) > 0)
{
if(dcmp(seg[i].x - y) > 0) return -1;
++ cnt, x = y;
if(dcmp(x - L) >= 0) return cnt;
}
y = std::max(y, seg[i].y);
}
if(dcmp(y - L) < 0) return -1;
return cnt + 1;
}
int main()
{
while(scanf("%d%lf%lf", &N, &L, &W) == 3)
{
input();
printf("%d\n", process());
}
return 0;
}