５１ ｎｏｄ 1298 圆与三角形 【计算几何】

#include <iostream>#include <cstdio>using namespace std;typedef long long ll;typedef struct {    ll x, y;} Point;Point A, B, C, O;ll r;ll distance(Point *p_1, Point *p_2) {    return (p_1->x - p_2->x) * (p_1->x - p_2->x) + (p_1->y - p_2->y) * (p_1->y - p_2->y);}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;//  判断是否相交，相交返回1，否则返回0}int intersect() {    ll distA = distance(&O, &A);    //  OA^2    ll distB = distance(&O, &B);    //  OB^2    ll distC = distance(&O, &C);    //  OC^2    ll r2 = r * r;                  //  r^2    if (distA < r2 && distB < r2 && distC < r2) {       //  圆包含三角形        return 0;    } else if (distA > r2 && distB > r2 && distC > r2) { //  三点都在圆外        return segOnCircle(&A, &B) || segOnCircle(&A, &C) || segOnCircle(&B, &C);   //  都不相交返回0，反之，返回1    }    return 1;}int main() {    int t;    scanf("%d", &t);    while (t--) {        scanf("%lld%lld%lld%lld%lld%lld%lld%lld%lld", &O.x, &O.y, &r, &A.x, &A.y, &B.x, &B.y, &C.x, &C.y);        printf("%s\n", intersect() ? "Yes" : "No");    }    return 0;}