HDU 6697 Closest Pair of Segments（线段距离）

  1 //        ——By DD_BOND
  2 
  3 //#include<bits/stdc++.h>
  4 //#include<unordered_map>
  5 //#include<unordered_set>
  6 #include<functional>
  7 #include<algorithm>
  8 #include<iostream>
  9 //#include<ext/rope>
 10 #include<iomanip>
 11 #include<climits>
 12 #include<cstring>
 13 #include<cstdlib>
 14 #include<cstddef>
 15 #include<cstdio>
 16 #include<memory>
 17 #include<vector>
 18 #include<cctype>
 19 #include<string>
 20 #include<cmath>
 21 #include<queue>
 22 #include<deque>
 23 #include<ctime>
 24 #include<stack>
 25 #include<map>
 26 #include<set>
 27 
 28 #define fi first
 29 #define se second
 30 #define MP make_pair
 31 #define pb push_back
 32 
 33 #pragma GCC optimize(3)
 34 #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
 35 
 36 using namespace std;
 37 
 38 typedef long long ll;
 39 
 40 const int MAXN=1e5+10;
 41 const double eps=1e-8;
 42 const double pi=acos(-1.0);
 43 const ll INF=0x3f3f3f3f3f3f3f3f;
 44 
 45 inline int dcmp(double x){
 46     if(fabs(x)<eps)    return 0;
 47     return (x>0? 1: -1);
 48 }
 49 
 50 inline double sqr(double x){ return x*x; }
 51 
 52 struct Point{
 53     double x,y; int id;
 54     Point(){ x=0,y=0; }
 55     Point(double _x,double _y):x(_x),y(_y){}
 56     void input(){ scanf("%lf%lf",&x,&y); }
 57     void output(){ printf("%.2f %.2f\n",x,y); }
 58     inline bool operator <(const Point &b)const{
 59         return (dcmp(x-b.x)==0? dcmp(y-b.y)<0 : x<b.x);
 60     }
 61     inline Point operator -(const Point &b)const{
 62         return Point(x-b.x,y-b.y);
 63     }
 64     inline double len2(){    //长度平方
 65         return sqr(x)+sqr(y);
 66     }
 67     inline double len(){   //长度
 68         return sqrt(len2());
 69     }
 70 };
 71 
 72 inline double cross(Point a,Point b){    //叉积
 73     return a.x*b.y-a.y*b.x;
 74 }
 75 
 76 inline double dot(Point a,Point b){    //点积
 77     return a.x*b.x+a.y*b.y;
 78 }
 79 
 80 inline double dis(Point a,Point b){    //两点的距离
 81     Point p=b-a;    return p.len();
 82 }
 83 
 84 struct Line{
 85     Point s,e;
 86     Line(){}
 87     Line(Point _s,Point _e):s(_s),e(_e){} //两点确定直线
 88     void input(){
 89         s.input();
 90         e.input();
 91     }
 92     double length(){
 93         return dis(s,e);
 94     }
 95 };
 96 
 97 inline double point_to_line(Point p,Line a){    //点到直线距离
 98     return fabs(cross(p-a.s,a.e-a.s)/a.length());
 99 }
100 
101 inline double point_to_seg(Point p,Line a){    //点到线段距离
102     if(dcmp(dot(p-a.s,a.e-a.s))<0||dcmp(dot(p-a.e,a.s-a.e))<0)
103         return min(dis(p,a.e),dis(p,a.s));
104     return point_to_line(p,a);
105 }
106 
107 inline double seg_to_seg(Line u,Line v){
108     return min( min(point_to_seg(u.s,v),point_to_seg(u.e,v)), min( point_to_seg(v.s,u),point_to_seg(v.e,u)) );
109 }
110 
111 Line line[MAXN];
112 
113 bool cmp(Line a,Line b){
114     return a.s<b.s;
115 }
116 
117 int main(void){
118     int T;  scanf("%d",&T);
119     while(T--){
120         int n;  scanf("%d",&n);
121         for(int i=0;i<n;i++){
122             line[i].input();
123             if(line[i].e<line[i].s) swap(line[i].s,line[i].e);
124         }
125         sort(line,line+n,cmp);
126         double ans=1e10;        
127         for(int i=0;i<n;i++)
128             for(int j=i+1;j<n;j++){
129                 if(dcmp(line[j].s.x-line[i].e.x-ans)>0)    break;
130                 ans=min(ans,seg_to_seg(line[i],line[j]));
131             }
132         printf("%.12f\n",ans);
133     }
134     return 0;
135 }