POJ 1328 Radar Installation 貪心算法

代碼如下：

// 貪心算法

#include<iostream>
#include<algorithm>
#include<math.h>
using namespace std;

// 包含左右端點
struct interval{
	double left;
	double right;
};
interval intervals[1002];
double d;
int n;

bool cmp(interval&a, interval&b){
	return a.left < b.left;
}

int main(int argc, char* argv[])
{
	int case_num = 0;
	while (scanf("%d%lf", &n, &d) && (n||d) ){
		case_num++;
		bool has_solution = true;
		for (int i = 0; i < n; i++){
			double x, y;
			scanf("%lf%lf", &x, &y);
			if (fabs(y) > d) 
				has_solution = false;
			else{
				intervals[i].left = x - sqrt(d*d - y*y);
				intervals[i].right = x + sqrt(d*d - y*y);
			}
		}
		if (has_solution == false)
		{
			cout << "Case " << case_num << ": " << -1 << endl;
			continue;
		}
		// 對所有區間進行排序
		sort(intervals, intervals + n, cmp);

		// 
		int num_radars = 1;
		double cur_radar = intervals[0].right;
		for (int i = 0; i < n; i++){
			if (intervals[i].left <= cur_radar)
			{
				if (intervals[i].right < cur_radar)
					cur_radar = intervals[i].right;
			}
			else
			{
				num_radars++;
				cur_radar = intervals[i].right;
			}
		}

		cout << "Case " << case_num << ": " << num_radars << endl;
	}
	return 0;
}