隨機增量算法（a randomized incremental algorithm）

#define sqr(x) ((x)*(x)) #define EPS 1e-4struct P{double x, y;P(double x, double y):x(x),y(y){}P(P &a, P &b):x(b.x-a.x),y(b.y-a.y){}P(){}P mid(P &a){return P((a.x+x)/2, (a.y+y)/2);}double cross(P &a){return x*a.y-y*a.x;}double len2(){return sqr(x)+sqr(y);}double dis(P &a){return sqrt(sqr(x-a.x)+sqr(y-a.y));}void print(){printf("%f %f\n", x, y);} };struct Disc{P o;double r;bool cover(P &a){return r-o.dis(a) >= -EPS;}Disc(){}Disc(P &o, double r):o(o),r(r){}Disc(P &a, P &b):o(a.mid(b)), r(a.dis(b)/2){}Disc(P &a, P &b, P &c){double t1=b.len2()-a.len2();double t2=c.len2()-a.len2();P p1(a, b), p2(a, c);double t3=p1.cross(p2)*2;P p3(t1, p1.y), p4(t2, p2.y);P p5(p1.x, t1), p6(p2.x, t2);o=P(p3.cross(p4)/t3, p5.cross(p6)/t3);r=o.dis(a);} };Disc MinDisc(vector<P> &p){if(p.size()<=1) return Disc();random_shuffle(p.begin(), p.end());Disc d(p[0], p[1]);for(int i=2; i<p.size(); i++)if(!d.cover(p[i])){d=Disc(p[0], p[i]);for(int j=1; j<i; j++)if(!d.cover(p[j])){d=Disc(p[i], p[j]);for(int k=0; k<j; k++)if(!d.cover(p[k]))d=Disc(p[i], p[j], p[k]);}}return d; }

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轉載于:https://www.cnblogs.com/Patt/p/4975878.html

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