【YBTOJ】【贪心】雷达装置

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思路：

贪心
坐标范围可以用勾股来确定
-1的判断就看纵坐标是否大于半径即可

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$Code$:

#include <cmath>
#include <cstdio>
#include <iostream>
#include <algorithm> 
#define rr register
using namespace std;

int n, d, ans = 1,x[1001],y[1001];
struct node {
    
    double l,r;}e[10005];
bool cmp (node xx,node yy){
    
    xx.r < yy.r;}//排序
int main ()
{
    
    
	scanf ("%d%d", &n, &d);
	for (rr int i = 1; i <= n; ++i)
	{
    
    
		scanf("%d%d",&x[i],&y[i]);
		if (abs(y[i]) > d){
    
    printf("-1");return 0;}
		e[i].l = (double)x[i] - (double) sqrt(d * d - y[i] * y[i]);//勾股确定范围
		e[i].r = (double)x[i] + (double) sqrt(d * d - y[i] * y[i]);
	}
	sort(e + 1 , e + 1 + n , cmp);
	double now = e[1].r;
	for(rr int i = 2; i <= n; ++i)
	{
    
    
		if(e[i].l <= now && now <= e[i].r) continue;//贪心找最优解
		else {
    
    ans++; now = e[i].r;}
	}
	printf("%d", ans);
	return 0;
}