UVA1615 高速公路 Highway

#include <iostream>
#include <cmath>
#include <algorithm>
#include <cstdio>
using namespace std;
typedef long long ll ;
typedef double db ;
const db eps = 1e-4 ;
const int N = 1e5 + 1 ;
double L , D ;
int n ;
int check ( db x , db y ) {
	if ( fabs ( x - y ) < eps )return 0 ;
	return 1 ;
}
struct node {
	db l , r ;
	node ( db x = 0 , db y = 0 ) : l ( x ) , r ( y ) {}
	bool operator < ( const node & rhs ) {
		if ( check ( r , rhs . r ) == 0 ) return l < rhs . l ; 
		return r < rhs . r ; 
	}
	void read ( db x , db y , db d ) {
		double sq = sqrt ( d * d - y * y ) ;
		l = x - sq ;r = x + sq ;
		l = l < 0.000 ? 0.000 : l ;
		r = r > L ? L : r ;
		return ;
	}
} point [ N ] ;
int main ( ) {
	/*
	freopen ( "text.in" , "r" , stdin ) ;
	freopen ( "text.out" , "w" , stdout ) ;
	*/
	WORK:
	if ( scanf ( "%lf%lf%d" , & L , & D , & n ) == EOF ) return 0 ;
	for ( int i = 0 ; i < n ; i ++ ){
		static double x , y ;
		scanf ( "%lf%lf" , & x , & y ) ;
		point [ i ] . read ( x , y , D ) ;
	}
	sort ( point , point + n ) ;
	int ans = 1 ; db now = point [ 0 ] . r ;
	for ( int i = 1 ; i < n ; i ++ ) {
		if ( point [ i ] . l > point [ i ] . r ) continue;
		if ( check ( point [ i ] . l , point [ i - 1 ] . l ) == 0 || check ( point [ i ] . l , now ) == 0 ) 
			continue;
		if ( point [ i ] . l > now ) now = point [ i ] . r , ans ++ ;
	}
	printf ( "%d\n" , ans ) ;
	goto WORK;
	return 0 ; 
}