51 lines
1.2 KiB
C++
51 lines
1.2 KiB
C++
#include <iostream>
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#include <cstdio>
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#include <cstring>
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#include <cstdlib>
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#include <cmath>
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#include <algorithm>
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#define eps 1e-8
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using namespace std;
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#define N 10007
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int sgn(double x)
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{
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if(x > eps) return 1;
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if(x < -eps) return -1;
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return 0;
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}
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int main()
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{
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double Rm,R,r,x,y,vx,vy;
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while(scanf("%lf%lf%lf%lf%lf%lf%lf",&Rm,&R,&r,&x,&y,&vx,&vy)!=EOF)
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{
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double A1 = (vx*vx+vy*vy);
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double B1 = (2*vx*x+2*y*vy);
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double C1 = x*x+y*y-(R+r)*(R+r);
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double A2 = A1;
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double B2 = B1;
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double C2 = x*x+y*y-(Rm+r)*(Rm+r);
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double delta1 = B1*B1 - 4.0*A1*C1;
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double delta2 = B2*B2 - 4.0*A2*C2;
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if(sgn(delta1) <= 0)
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{
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puts("0.000");
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continue;
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}
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double J11 = (-B1 + sqrt(delta1))/(2.0*A1);
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double J12 = (-B1 - sqrt(delta1))/(2.0*A1);
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if(sgn(J12) >= 0)
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{
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if(sgn(delta2) <= 0)
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{
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printf("%.3f\n",fabs(J11-J12));
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continue;
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}
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double J22 = (-B2 - sqrt(delta2))/(2.0*A2);
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printf("%.3f\n",(J22-J12)*2.0);
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}
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else
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puts("0.000");
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}
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return 0;
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}
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