AOJ

# # Problem

http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_7_D

# # Explanation

Refer the link below for algorithm

Cross points of a line and a circle

# # Solution

Int N;
double R;
Vector2 C, p1, p2;

Vector2 project(Vector2 start_, Vector2 end_, Vector2 p) {
Vector2 v = end_ - start_;
return start_ + v * (v.dot(p - start_) / v.norm());
}

Vector2 unitVec(Vector2 v) {
return v / v.length();
}

pair<Vector2, Vector2> crossPoints() {
Vector2 p = project(p1, p2, C);
Vector2 e = unitVec(p2 - p1);
double len = sqrt(R*R - (p - C).norm());
Vector2 x1 = p + e * len;
Vector2 x2 = p + e * (-len);
if (fabs(x1.x) < EPS) x1.x = 0.0;
if (fabs(x1.y) < EPS) x1.y = 0.0;
if (fabs(x2.x) < EPS) x2.x = 0.0;
if (fabs(x2.y) < EPS) x2.y = 0.0;
if (x1 < x2) return make_pair(x1, x2);
return make_pair(x2, x1);
}

void solve() {
auto points = crossPoints();
cout << points.first.x << ' ' << points.first.y << ' ';
cout << points.second.x << ' ' << points.second.y << endl;
}

void input() {
cin >> C >> R >> N;
while (cin >> p1 >> p2) {
solve();
}
}

int main() {
cout.precision(15);
input();
}


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