判断线段与圆是否相交

ACM模版

判断线段与圆是否相交

typedef long long ll;
typedef struct  // 点结构
{
    ll x, y;
} Point;

Point A, B, C, O;   // 三角形三点与圆心
ll r;               // 半径

// 判断线段是否和圆相交
int segOnCircle(Point *p_1, Point *p_2)
{
    ll a, b, c, dist_1, dist_2, angle_1, angle_2;   // ax + by + c = 0;
if (p_1->x == p_2->x)                           // 当x相等
    {
        a = 1, b = 0, c = -p_1->x;
    }
else if (p_1->y == p_2->y)                      // 当y相等
    {
        a = 0, b = 1, c = -p_1->y;
    }
else
    {
        a = p_1->y - p_2->y;
        b = p_2->x - p_1->x;
        c = p_1->x * p_2->y - p_1->y * p_2->x;
    }
    dist_1 = a * O.x + b * O.y + c;
    dist_1 *= dist_1;
    dist_2 = (a * a + b * b) * r * r;
if (dist_1 > dist_2)
    {
return 0;
    }
    angle_1 = (O.x - p_1->x) * (p_2->x - p_1->x) + (O.y - p_1->y) * (p_2->y - p_1->y);
    angle_2 = (O.x - p_2->x) * (p_1->x - p_2->x) + (O.y - p_2->y) * (p_1->y - p_2->y);
if (angle_1 > 0 && angle_2 > 0)
    {
return 1;
    }
return 0;
}