洛谷P1325 雷达安装

题目

考虑对于一个小岛，如果有雷达可以覆盖它，则这些雷达肯定在一个区间里，则原题内容则变为区间选点问题

#include <bits/stdc++.h>
using namespace std;
int n, d, cnt;
struct data {
	double l, r;
}a[1001000];
bool cmp(data a, data b)
{
	if (a.r == b.r)
		return a.l > b.l;
	return a.r < b.r;
}
map <int, int> vis;
int main()
{		
	int ans = 1;
	scanf("%d%d", &n, &d);
	for (int i = 1; i <= n; i++)
	{	
		double x, y;
		scanf("%lf%lf", &x, &y);
		a[i].l = x - sqrt(d * d - y * y);
		a[i].r = x + sqrt(d * d - y * y);
	}	
	sort(a + 1, a + 1 + n, cmp);
	int now = a[1].r;
	for (int i = 2; i <= n; i++)
	{	
		if (a[i].l >= now)
			ans++, now = a[i].r;
	}	
	printf("%d", ans);
	return 0;
}