1 #include <bits/stdc++.h> 2 #define ll long long 3 using namespace std; 4 5 inline int read(){ 6 int x=0,f=1; char ch=getchar(); 7 while(ch<'0'||ch>'9'){ if(ch=='-') f=-1; ch=getchar(); } 8 while(ch>='0'&&ch<='9'){ x=(x<<1)+(x<<3)+(ch^48); ch=getchar();} 9 return x*f; 10 } 11 12 inline void write(int x){ 13 if(x<0){ 14 putchar('-'); 15 x=-x; 16 } 17 if(x>9){ 18 write(x/10); 19 } 20 putchar(x%10+'0'); 21 } 22 23 double X,Y,R; 24 double p_x1,p_y1,p_x2,p_y2; 25 26 int judge(double a,double b){ //判断点在不在圆内圆上 27 double shu1=R*R,shu2=(a-X)*(a-X)+(b-Y)*(b-Y); 28 if(shu1>shu2) return -1; //圆内 29 else if(shu1==shu2) return 0; //圆上 30 else return 1; //圆外 31 } 32 33 34 int main(){ 35 while(scanf("%lf%lf%lf",&X,&Y,&R)!=EOF){ 36 scanf("%lf%lf%lf%lf",&p_x1,&p_y1,&p_x2,&p_y2); 37 int flag1=judge(p_x1,p_y1),flag2=judge(p_x2,p_y2); 38 bool flag=false; 39 if(flag1==0||flag2==0) flag=true; //有一个在圆上 40 else if(flag1==-1&&flag2==-1) flag=false; //两个都在圆内 41 else if((flag1==1&&flag2==-1)||(flag1==-1&&flag2==1)) flag=true; //一个在圆内 一个在圆外 42 else{ 43 double A,B,C; 44 if(p_x1==p_x2) A=1,B=0,C=-p_x1; 45 else if(p_y1==p_y2) A=0,B=1,C=-p_y1; 46 else A=p_y2-p_y1,B=-(p_x2-p_x1),C=-p_x1*p_y2+p_x2*p_y1; 47 double shu1=(A*X+B*Y+C)*(A*X+B*Y+C); 48 double shu2=A*A+B*B; 49 if(shu1<=R*R*shu2){ 50 double eex=X-p_x1,eey=Y-p_y1,rrx=p_x2-p_x1,rry=p_y2-p_y1; 51 double angleone=eex*rrx+eey*rry; 52 eex=X-p_x2,eey=Y-p_y2,rrx=p_x1-p_x2,rry=p_y1-p_y2; 53 double angletwo=eex*rrx+eey*rry; 54 if(angleone>0&&angletwo>0) flag=true; 55 } 56 57 } 58 if(!flag) printf("The line segment does not intersect the circle. "); 59 else printf("The line segment intersects the circle. "); 60 } 61 62 return 0; 63 } 64 65