題意：

給出兩個(gè)線段的端點(diǎn)，讓你求這兩條線段的最近距離和最遠(yuǎn)距離。

思路：

最近距離只可能出現(xiàn)在端點(diǎn)到垂足或者端點(diǎn)到端點(diǎn)上，最長(zhǎng)距離只會(huì)出現(xiàn)在端點(diǎn)到端點(diǎn)上。

代碼：

#include<cstdio> #include<cstring> #include<climits> #include<cmath> #include<cstdlib> #include<iostream> #include<algorithm> #include<string> #include<queue> #include<map> #include<vector> #include<set> #include<sstream>using namespace std;const double eps = 1e-5; const int maxn=10000;int cmp(double x) {if(fabs(x) < eps) return 0;if(x > 0) return 1;return -1; }struct point {double x, y;point() {};point(double a, double b) : x(a), y(b) {};friend point operator + (const point & a, const point &b){return point(a.x + b.x , a.y + b.y );}friend point operator - (const point & a, const point &b){return point(a.x - b.x, a.y - b.y);}friend point operator * (const point & a, const double &b){return point(a.x * b, a.y * b);}friend point operator / (const point & a, const double &b){return point(a.x / (b+eps), a.y / (b + eps));}friend bool operator == (const point& a, const point& b){return cmp(a.x - b.x) == 0 && cmp(a.y - b.y) == 0;}double norm(){return sqrt(x*x + y*y);} };double det(const point &a,const point &b) {return a.x * b.y - a.y * b.x; }double dot(point a, point b) {return a.x * b.x + a.y * b.y; } void PointPro(point p,point s,point t,point &cp) {double r = dot((t - s),(p - s))/dot(t-s,t - s);cp = s + (( t - s) * r); }bool On(point p, point s, point t) {return cmp(det(p-s, t - s)) == 0&& cmp(dot(p-s,p-t))<=0; }struct polygon {int n;point a[maxn];polygon() {};double area(){ // printf("nnnnnnnnnnnnnnnnnnnnnnnn%d\n", n);double sum = 0;a[n] = a[0];for(int i = 0; i < n; i++){ // puts("JJJJJ");sum += det(a[i + 1], a[i]);}return sum / 2;}point center(){point ans = point(0, 0); // printf("a = %lf\n",area());if(cmp(area()) == 0) return ans;a[n] = a[0];for(int i = 0; i < n; i++){ans = ans +(a[i] + a[i + 1]) * det(a[i + 1], a[i]);}return ans / area() / 6.0;} };double dis(point a,point b) {return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y)); }double dis_point_segment(const point& p, const point& s, const point& t) {if(cmp(dot(p-s, t-s))<0) return (p-s).norm();if(cmp(dot(p-t, s-t))<0) return (p-t).norm();return fabs(det(s-p, t-p)/(s-t).norm()); }struct line {point a, b;line(const point& a, const point& b) : a(a), b(b) {} };bool line_jiao(line a, line b) {bool res=true;res=res&&(cmp(det(a.b-a.a,b.a-a.a))*cmp(det(a.b-a.a,b.b-a.a))<0);res=res&&(cmp(det(a.a-a.b,b.a-a.b))*cmp(det(a.a-a.b,b.b-a.b))<0);res=res&&(cmp(det(b.b-b.a,a.a-b.a))*cmp(det(b.b-b.a,a.b-b.a))<0);res=res&&(cmp(det(b.a-b.b,a.a-b.b))*cmp(det(b.a-b.b,a.b-b.b))<0);return res; }double _max(double a,double b) {if(cmp(a-b)>0)return a;return b; }double _min(double a,double b) {if(cmp(a- b)>0)return b;return a; }int main() {//freopen("in.txt","r",stdin);//printf("%d\n",line_jiao(line(point(0,0),point(2,0)),line(point(1,1),point(1,-1))));point a,b,c,d;int cas=1;while(scanf("%lf%lf%lf%lf%lf%lf%lf%lf",&a.x,&a.y,&b.x,&b.y,&c.x,&c.y,&d.x,&d.y)!=EOF){double minans=1000000000000.0;double maxans=-1000000000000.0;minans=_min(minans,dis_point_segment(a,c,d));minans=_min(minans,dis_point_segment(b,c,d));minans=_min(minans,dis_point_segment(c,a,b));minans=_min(minans,dis_point_segment(d,a,b));minans=_min(minans,dis(a,c));minans=_min(minans,dis(a,d));minans=_min(minans,dis(b,c));minans=_min(minans,dis(b,d));if(line_jiao(line(a, b), line(c, d)))minans=0.0;maxans=_max(maxans,dis(a,c));maxans=_max(maxans,dis(a,d));maxans=_max(maxans,dis(b,c));maxans=_max(maxans,dis(b,d));if(a==b&&c==d)minans=maxans;printf("Case #%d: %.3lf %.3lf\n",cas++,maxans,minans);}return 0; }

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