ZOJ 1041Transmitters

 雖然歸屬於search problems，但是用簡單的方法就可以做了。所有的長度都是double，用int就錯了。scanf讀取double應該用%lf，用%f g++會讀取錯誤。這種浮點數計算，儘量不要用除法、開方，改成乘法。用atan2不知道算不算錯，反正改成了叉乘了。最後輸出的時候錯誤地+1，導致浪費了很多時間。 

 

//ZOJ1041Transmitters
#include <iostream>
#include <stdio.h>
#include <math.h>
//#define DEBUG
using namespace std;

int main(int argc, char *argv[])
{
        double tr[2], radius, pt[155][2], pt_tmp[2], dist_tmp[2];
        int pt_sum, pt_r_sum, same_count[155], max_count;
        double base_angle, angle, angle_diff;
        while (scanf("%lf%lf%lf", &tr[0], &tr[1], &radius) && radius >= 0)
        {
                scanf("%d", &pt_sum);
#ifdef DEBUG
                //cout << tr[0] << " " << tr[1] << " " << radius << " " << pt_sum << endl;
#endif
                if (pt_sum == 0)
                {
                        cout << 0 << endl;
                        continue;
                }
                pt_r_sum = 0;
                for (int i = 0; i < pt_sum; i ++)
                {
                        cin >> pt_tmp[0] >> pt_tmp[1];
                        dist_tmp[0] = (pt_tmp[0] - tr[0]);
                        dist_tmp[1] = (pt_tmp[1] - tr[1]);
                        if (dist_tmp[0] * dist_tmp[0] + dist_tmp[1] * dist_tmp[1]
                                <= radius * radius)
                        {
                                same_count[pt_r_sum] = 0;
                                pt[pt_r_sum][0] = pt_tmp[0];
                                pt[pt_r_sum][1] = pt_tmp[1];
                                pt_r_sum ++;
                        }
                }
                for (int i = 0; i < pt_r_sum; i ++)
                {
                        //base_angle = atan2(pt[i][1] - tr[1], pt[i][0] - tr[0]);
#ifdef DEBUG
                        cout << "pt " << i << " baseangle " << base_angle << endl;
#endif
                        for (int j = 0; j < pt_r_sum; j ++)
                        {
                                //if (j == i)
                                //      continue;
                                //angle = atan2(pt[j][1] - tr[1], pt[j][0] - tr[0]);
                                //angle_diff = angle - base_angle;
                                //if (angle_diff <= -M_PI)
                                //      angle_diff += 2.0 * M_PI;
                                //else if (angle_diff >= M_PI)
                                //      angle_diff -= 2.0 * M_PI;
#ifdef DEBUG
                                cout << "anglediff " << j << " " << angle_diff << endl;
#endif
                                //if (angle_diff >= 0)
                                if ((pt[i][0] - tr[0]) * (pt[j][1] - tr[1])
                                        - (pt[j][0] - tr[0]) * (pt[i][1] - tr[1]) >= 0)
                                {
                                        same_count[i] ++;
#ifdef DEBUG
                                        cout << "pt " << i << " same "
                                                << pt[j][0] << " " << pt[j][1] << endl;
#endif
                                }
                        }
                }
                max_count = 0;
                for (int i = 0; i < pt_r_sum; i ++)
                {
#ifdef DEBUG
                        cout << "pt " << i << " cnt " << same_count[i] << endl;
#endif
                        if (same_count[i] > max_count)
                                max_count = same_count[i];
                }
                printf("%d\n", max_count);
        }
        return 0;
}