G49 向量运算 点线关系【计算几何】

#include<bits/stdc++.h>
using namespace std;

const int N = 1e4 + 10;
struct Point
{
  int x, y;
} p[N], o, a;

double cross(Point a, Point b, Point c)
{ // 叉积
  return (b.x - a.x) * (c.y - a.y) - (b.y - a.y) * (c.x - a.x);
}
double dis(Point a, Point b)
{ // 距离
  return sqrt(1.0 * (a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));
}
int main()
{
  int n, m, ans;
  double r;
  while (scanf("%d%d%lf", &o.x, &o.y, &r) != EOF)
  {
    n = ans = 0;
    scanf("%d", &m);
    while (m--)
    {
      scanf("%d%d", &a.x, &a.y);
      if (dis(a, o) <= r)
        p[n++] = a;
    }
    for (int i = 0; i < n; i++)
    {
      int cnt = 0;
      for (int j = 0; j < n; j++)
        if (cross(o, p[i], p[j]) >= 0)
          ++cnt;
      ans = max(ans, cnt);
    }
    printf("%d\n", ans);
  }
  return 0;
}

G49 向量运算 点线关系【计算几何】

#include<bits/stdc++.h>
using namespace std;

const int N = 1e4 + 10;
struct Point
{
  int x, y;
} p[N], o, a;

double cross(Point a, Point b, Point c)
{ // 叉积
  return (b.x - a.x) * (c.y - a.y) - (b.y - a.y) * (c.x - a.x);
}
double dis(Point a, Point b)
{ // 距离
  return sqrt(1.0 * (a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));
}
int main()
{
  int n, m, ans;
  double r;
  while (scanf("%d%d%lf", &o.x, &o.y, &r) != EOF)
  {
    n = ans = 0;
    scanf("%d", &m);
    while (m--)
    {
      scanf("%d%d", &a.x, &a.y);
      if (dis(a, o) <= r)
        p[n++] = a;
    }
    for (int i = 0; i < n; i++)
    {
      int cnt = 0;
      for (int j = 0; j < n; j++)
        if (cross(o, p[i], p[j]) >= 0)
          ++cnt;
      ans = max(ans, cnt);
    }
    printf("%d\n", ans);
  }
  return 0;
}