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51nod 1298 圆与三角形——计算几何

题目链接：http://www.51nod.com/Challenge/Problem.html#!#problemId=1298

转化成判断三条线段和圆是否🍌相交就行了

 1 #include<cstdio>
 2 using namespace std;
 3 
 4 struct point { double x,y; };
 5 point A,B,C,O;
 6 double r;
 7 
 8 bool pan1(point P){///判断点是否在圆内
 9     if( (P.x-O.x)*(P.x-O.x) + (P.y-O.y)*(P.y-O.y) -r*r <=0)
10         return 1;
11     return 0;
12 }
13 bool pan2(point p1, point p2,double r) {///判线段是否与圆相交
14     if(pan1(p1)&&pan1(p2))//都在圆内 不相交
15         return 0;
16     if(!pan1(p1)&&pan1(p2)||pan1(p1)&&!pan1(p2))//一个圆内一个圆外 相交
17         return 1;
18 
19     //都在圆外
20     double a, b, c, dist1, dist2, angle1, angle2; // ax + by + c = 0;
21     if (p1.x == p2.x)//特殊情况判断，分母不能为零
22         a = 1, b = 0, c = -p1.x;
23     else if (p1.y == p2.y)//特殊情况判断，分母不能为零
24         a = 0, b = 1, c = -p1.y;
25     else {
26         a = p1.y - p2.y;
27         b = p2.x - p1.x;
28         c = p1.x * p2.y - p1.y * p2.x;
29     }
30     dist1 = a * O.x + b * O.y + c;
31     dist1 *= dist1;
32     dist2 = (a * a + b * b) * r * r;
33     if (dist1 > dist2) return 0;///点到直线距离大于半径r
34     angle1 = (O.x - p1.x) * (p2.x - p1.x) + (O.y - p1.y) * (p2.y - p1.y);
35     angle2 = (O.x - p2.x) * (p1.x - p2.x) + (O.y - p2.y) * (p1.y - p2.y);
36     if (angle1 > 0 && angle2 > 0) return 1;///余弦都为正，则是锐角
37     return 0;
38 }
39 
40 int main(){
41     int t; scanf("%d",&t);
42     while(t--){
43         scanf("%lf%lf%lf",&O.x,&O.y,&r);
44         scanf("%lf%lf%lf%lf%lf%lf",&A.x,&A.y,&B.x,&B.y,&C.x,&C.y);
45         if(pan2(A,B,r)||pan2(A,C,r)||pan2(B,C,r))
46             puts("Yes");
47         else
48             puts("No");
49     }
50     return 0;
51 }

 

posted @ 2019-01-31 13:01  noobimp  阅读(274)  评论(0)  编辑  收藏  举报